9 1/4 rear?

Lack of performance parts like spools and steeper gear ratios plus they have the floating axles which would require C clip eliminators or a change over to Dana/8.75 ends. I'm not sure of the axle spline either which I think is oddball.

There is some stuff out there for them and for a street car I would consider it if I had a complete one with the ratio I wanted. Otherwise it's probably more cost effective to go 8.75 or Dana 60 depending on your application.