Originally Posted by
nilak
Ive watched this presentation youtu.be/E0yZdLkpvR0 some while ago and these guys did some extensive research on this transmission. They say it can handle even 475lbft although its rated by the manufacturer dor a lower torque (I think 400lbft). But taking into account its now over 30 years old and 130k miles, I thought something like 400lbft would be better for reliability. Anyway 12% over 400lbft does seem a huge step, it could be safe.
Another problem can be the the C beam, but that basically depends on the output torque not input (engine) torque and I think can be a problem if you use drag tires even with std engine, 1&2 gears can generate enough torque up to race tires traction break up.