This comes from Mopar Enthusiasts Car Club of America. It's lengthy but some might find it useful.
Chrysler installed three different type rear ends in A-bodies from 63-76: the 7-1/4", the Spicer 8-1/4" and the Chrysler 8-3/4". The 7-1/4" was designated for light duty service. It served as the only rearend available from 1963-65, and from then on to 1976, the 7-1/4" was used in six cylinder and some lighter duty eight cylinder applications. By far, the 7-1/4" accounts for the majority of A-body rear ends produced. The 8-3/4" was introduced in 1966 for heavy duty applications (Originally it was available in 1965 as a rear end that could be ordered by dealers and designated as a drag racing a rear end). The 8-3/4" was standard on the 340 and 383 A-bodies and optional as part of a heavy duty axle package on the other engines. When the 8-3/4" was discontinued (for the A-body) in 1973, its replacement for heavy duty A-body applications was the Spicer 8-1/4" rear end (a rear end Chrysler began using in B and C body cars as early as 1969).
Besides these three factory rear end swap options, there were are a number of different rear ends that A-body owners can adapt to their application. Below is a list of common swaps as well as more information on the three factory rear ends.
1973-76 Spicer 8-1/4" rear ends from 1973-76 A-bodies.
The 8-1/4" has 10 bolts holding an inspection plate to the rear of the housing. If you are looking to change your wheel pattern from a 5x4" to a 5x4.5", these are the cheapest route to go as they can be had for $100 or less. Swap meets will find sure-grip limited slip versions going for less than $200. The 8-1/4" rear can handle most 340/360 applications. NOTE: removal of axles requires pulling the rear inspection cover, removing the spider gears, pushing the axles inward, and pulling out the C-clip axle retainers.
1966-72 Chrysler 8-3/4".
This was the corporate rear end for passenger cars from 1957-1974. It was adapted to the A-body in 1966. You can find more information about these rear ends in Gary Lewallen (aka. Vaanth)'s excellent 8-3/4" Rear Axle Guide. The A-body 8-3/4" became available in 1965, but as a dealer installed option only, and it was billed by the Chrysler bulletin as a "drag racing rear end" only made available with drag racing gears. It is not certain that the rearend available from the dealer in 1965 was the same width as the 66-72 8-3/4" as the bulletin stated that "wheels with additional offset are required."
8-3/4" rear ends are indentified by their casting number on the side of the case and it is by the last three digits of this casting number that the cases are commonly known ( 741, 742, 489 ).
All of the A-body 8-3/4's were small bolt pattern axles (5x4") without exception. These rear ends can be converted to the larger wheel pattern axles by shortening and resplining long axles (from a C-body or truck). The donor vehicles to look for are 72-74 D100 trucks, and early 70's C-body wagons with straight axles ( the tapered axles are unusable ). The donor axles must have a fat enough outside diameter so that new splines can be cut. If you measure from the outside of the wheel stud flange up the axle 28", this is where the axle will be cut and re-splined. There are several machine shops that can do this, check with local 4x4 axle shops, or look for advertisements in mopar magazines. Salvage yard prices on the axles run $15-50/pair and the machine work is about $100 including shipping (Moser).
Another 8-3/4" option is to use a B-body 8-3/4" rear end. There were several different widths used in B-bodies during the sixties. The 1962-63 B-body rear measured 53-1/4", It was changed in 64,65,66,and again in 68. The 68-70 was approximately 55" wide. 1971 and later B-bodies are too wide of candidates. On Dusters and Dart Sports, the wider rearend looks at home. On early A-bodies (1963-66) its looks a little awkward. While the 1962-63 rear end is only a sanct 3/4" wider than an A-bodies, its downside is that the 1962-64 rear end uses a tapered axle that can be difficult to work with.
All the 1962-70 B-body rear ends came with their spring perches 44" apart, whereas the A-bodies were 43" apart. With any B-body rearend you will need to move the spring perches inward 1/2" on both sides.
A conversion to the larger 5x4.5" pattern wheels that is somewhat common is redrilling the original small pattern axles and installing new lugs to facilitate a larger diameter wheel. The problem with this is that there isn't enough meat on the axle flanges to drill a hole for a regular splined lug and cap screws must be used. Racers have been doing this for years, so its not necessarily a dangerous move. It is safe to say that it is the most "un-elegant" 8-3/4" solution for A-bodies. In addition, the original SBP 10x1.75" brake drums must also be redrilled. You cannot use drum setups from 5x4.5" axles (No exceptions) with redrilled small pattern A-body axles.
A few final notes on the 8-3/4" rear ends: The 2 spring shackles that mount the axle to the springs via 4 U-bolts are a different size than the 7-1/4" units. This is because the axle tubes for the 8-3/4" are of a larger diameter. These shackle plates can be found on any 8-3/4" equipped car, and have recently been re-introduced by a Mopar Performance©. While on the topic of U-bolts, one should not reuse U-bolts. They are designed for a one-time use and the threads are distorted once installed the first time. These are cheap and can be ordered from many parts houses including ESPO Springs, and probably your local parts counter, for $10-15 a set.
The Spicer built 7-1/4"
This rear end was the smallest, lightest, and most common A-body rear end. This rear end is often, if not always bashed by Mopar fans. However, Standard on all sixes and most v8's though to 1972, this rearend is extremely common. Since most people move away from this rear end, I won't say much about it. Unlike its bigger brother, the Spicer 8-1/4", the 7-1/4" does not require the removal of the inspection plate to pull the rear axles. The upshot is that if you have a slant six A-body and you want to replace your howling 7-1/4", a "want ad" in your local mopar club publication will have people practically giving 7-1/4"s to you. Early 7-1/4"s used 9 bolts to hold the rear inspection cover. Factory ratios included (but were not limited to) 2.93, 3.23, and 3.91 ratios and Sure grips were optional. Most 170cid sixes (automatic and manual transmissions) as well as 225cid sixes with manual transmissions from 1963-1969 used a 3.23 ratio 7-1/4".
From 1960 to 1975, A-body 7-1/4"s used the small A-body 5x4" BC lug pattern. In 1976 (perhaps on some 1975 models as well), the 7-1/4" incorporated the larger 5x4.5" BC lug pattern. Some changes occured with the wheel bearing size and bearing retainer plate so these later 5x4.5" flanged axles do not fit in the earlier 5x4" axle housings. At some point C-clips were added to the 7-1/4". The 7-1/4" continued in A-bodies until 1976. They were later available in some F-bodies.
Spicer 9-1/4"
From the Gee, I never thought of that department, Moser Engineering can perform a unique operation on a Spicer 9-1/4" rear end (this rear end replaced the 8-3/4 on the heavy duty applications in 1974, such as C-bodies, police cars, and trucks). Moser can take a 9-1/4" rear end, pull the axles, cut the ends off and graft on some 8-3/4" ends, then cut and re-spline some C-body 8-3/4" axles, add "green bearings" rear end. The end result could be a 9-1/4" tucked under your A-body. Mopar Action ran a tech special on this very conversion about 10 years ago.
One important note about the A-body rear ends. All three factory rear ends (7-1/4", 8-1/4", 8-3/4") had different length pinion snouts, and each one requires a different length driveshaft. Also realize that there were different wheelbase A-bodies (111" and 108"), so driveshaft lengths will vary with that as well.
