Wanted 8 & 3/4 rear end for roadrunner

Any 71-74 B rear should work OK. 63" total axle to axle

You could grab:
C BODY
'65-'69= 61.75"
'70-'71= 63.0" (Chrysler & Fury)

IMPERIAL
'65-'66= 61 15/16"
'67-'69= 62 5/16"

E BODY
'70-'74= 61 5/8"

A100
'65-'70= 61 3/4"

D100
'65-'71= 63 15/16"

Put the perches where you need them.