Run a 1970 B Body rear end factory length since 1973 in my 1971 Challenger. 1971 Transmissions and Rear Ends because of the changes Chrysler did are not my first choice unless it is a restoration.. Some aftermarket housing do not have a provision for a Pinion Snubber on the housing. If you are going to run big HP I would be looking at aftermarket with good axles, center section, bearings, yoke on and on. It all cost about the same. If you plan on selling the rear end in the future a factory rear end would sell easier to someone doing a restoration.