Rear end advice for racing with a 4 speed

Put a Dana 60 in it with a good Power Loc sure grip (not a trac Loc diff) and a good set of axles and never worry about it again.
I have a Dana out of a 3/4 ton Dodge truck narrowed to fit my Dart, it has the 1/4 inch thick axle tubes (a lot heavier than the car axles) and didn't lose any E.T. at all when I switched from the 8 3/4.