The factory style powerlock diff is really strong.

The one I built for my dad's road runner was probably the cheapest ever, lol. Bought the complete rear for $150 from under a '70s dodge truck IIRC. It came w/ a powerlock diff., good 3.54 gear, and surprisingly it had a 1350 yoke on it.
All I bought for it was new 35 spline axles, 35 spline side gear and rebuild kit for the diff., housing ends and perches...all from Dr. Diff. Good friend of mine narrowed it and welded it all up. Built it myself.

Did the same thing for the Dana under my other road runner. Craigslist Dana 60 from a '70s Ford truck (had a bad ring and pinion and the weaker tracklock diff.) for $125. Used 4.10 gear from moparts for $75, spool, axles, ends, 1350 yoke, and perches from Dr. Diff.