Need some guidance on transmission/flexplate/torque convertor

Need some guidance on transmission/flexplate/torque convertor

As someone who has done exactly what you're looking to do, I can tell you Professor Fate's comments are bang on. I would only add something to this:

Professor Fate said
5.9s were balanced via the flexplate (from the factory), and so used a neutral balanced torque convertor.

This is true for 5.9s from 1996 to 2003. From 1993 to 1995 they had a neutral flex plate and the weight on the torque converter. I suspect the good Professor already knows this based on the way he started his comment with "In '97, the 5.9 Magnum used a weighted flex plate..." but I'm just clarifying for you and any future member that reads this thread.

The other thing I'll say is regarding this:

Professor Fate said
Lockup/OD trannies (A518/46RH and later the 46RE) started showing up in '88- this is the TC you currently have and can't use.

Some early A500/42RH and A518/46RH transmissions did not have lockup converters. I'm not sure which of those didn't have lockup, all I know for sure is that the diesel transmissions (47RH) from 1993 and earlier did not have lockup. I also don't know if the non-lockup A500/42RH and A518/46RH would work in a 727, but my guess is it would work.