With all due respect to your trans guy (and not trying to start a whizzing contest), tearing down the T5 isn't the point. It's all about proper application, thus why I commented on torque rating. For every T5 that has failed there are probably hundreds, likely thousands, that have worked great. And they weren't just in GMs, but also in Fords, Jeeps, and probably others. Again, match the right part to the job.

The 383 guy made a bad choice to start with, he should have gone with a larger Tremec that could handle the probable 400+ ft. lbs. of torque he was generating. The WC V8 T5's are rated for around 300 ft. lbs. Placed behind the right engine, with the proper gearing, they're a readily available, comparatively cheap, dependable transmission, especially if someone is going after the O/D for mileage reasons in addition to more flexibility in rear gear choices.