Sam,
Hey, perhaps the common link we share with similar experiences and outcomes starts with what's in front of the transmission twisting stock Jag differentials apart in the first place.
Possible Answer: knowledgeable FE engine builders that know how to make torque. Tom built mine, Keith built yours. The result was the weakest link gave out. Hopefully your 3rd round upgrades hold this time. If not, it might lead me to investigating a whole new rear subframe and IRS/differential design. I would possibly do it if there enough of us interested in it and making it worth doing at some point down the road.