[joyridin']

The issue isn’t really when they were built as much as everybody calls them something different. The yellow case is a series 1. It should have tapered bearings for the stub axles. It uses series 1 brakes due to having the bolt-on bracket for the caliper. I would have to check, but the other one is a series 1.5 or 2 due to the stub axle having the bolt holes integral in the housing...or at least it looks that way from what I can see. The differential housing changes slightly also.

Regardless of which one you use, you really want to use the case that has tapered roller bearings for the stub axles. The ball bearing style used in 1968-72 are not acailable anymore.