The OP states the rules require a GM rear end in a GM car, but don't specify a year range. That seems to leave the door open for the 9.3 Pontiac rear. Sounds like a ford 9" would not be allowed. I have installed a 3.42 and a 3.73 in the OE 65-70 full size housings. 4:11 and 4:30 I have never had my hands on although they were supposed to exist. Finding a set would be one heck of a find. Other than being very expensive to build, I like the 9.3" Pontiac rear. Stronger/Better than a Ford 9"? Personally, I don't think so. The extra support bearing on the pinion in a Ford 9" is a deflection game changer IMO. I do know the 9.3" cost more than twice as much as a Ford to rebuild with new parts. I recently replaced the limited slip unit, ring and pinion 3.42:1 and bearings and gaskets in my 9.3. About $1700.00 in parts from Fabcraft. I appreciate that they are still in business and have the parts, but they are expensive if your on a budget.
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