Big Bolt Rears

pacuda59 said
This comes from Mopar Enthusiasts Car Club of America. It's lengthy but some might find it useful.
...
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.

On my '73 Dart I went from a 7-1/4" to a 8-3/4" and had to shorten the driveshaft a bit.
Later on I shortened it again when I went from a 904 transmission to an A518.

I haven't had the shaft balanced yet since I can still take the car upto 80mph with my 3.9:1 gears. Little higher and a slight vibration becomes noticable.

Not that hard to do with some moderate skills;