I was planning on keeping the existing 9" rear end in our '69 Mach 1, and just doing a gear change (4.11 to something more like 3.50 so it can be driven on the highway). This weekend we went to tear the drum brakes off to start on a disc conversion and ran into a few concerns along the way, now I'm looking at replacing the whole rear with something new and known.
I'm looking at a Moser M9 with a Detroit Tru-Trac helical differential, 3.50 gears, and 31 spline axles. I noticed the 35 splines are roughly the same cost. I tend to overbuild/overspec everything for peace of mind, and since this isn't a drag car I'm not too worried about any minor weight addition. There won't be any hard dragstrip launches, so 31 spline torque limits calculate well within what I think this car will ever put down.
Any advice? Anything else I should consider? The car has a Cal-trac setup at the moment, which I figured I'd keep as-is.