Posi Conversion
They can be converted to
large bolt pattern if needed. You will need to watch the length when buying..
chances are your 72 has a 5 on 4 bolt pattern (what we call the small bolt pattern)
somewhere around 73 they started using 5 on 4.5 (large bolt pattern)
it would be preffered to keep the same bolt pattern all the way around but not biggy if you don't
keep in mind that if your car has drum brakes up front and you wish to convert to discs later you will most likely end up with large bolt pattern disc brakes
now, when your told to "watch the length" he means that a 8 3/4 rear end for a B body will have longer axle tubes and the spring perches in a different place then a 8 3/4 rear end for a A body
it can be made to fit, for sure, but it will take some modifying
the one exception being the early B bodies (what was it, 65-67?) they should still need to have the spring perches moved but are only marginally wider and will fit even with stock A body backspacing on your wheels (though they will fill the wheel wells better)
