eddie,,,
Look thru summits catalog at their premium rebuild kits.... in them you will see what most of the rebuilders use... kevlar discs etc... better seals,, the torque convertor can be modified/vanes tig welded for greater durability... maybe a slightly higher stall speed
The real tricks come down to what the builders choice is and what works for them...I like the late model cases 87 and later... haynes makes a nice rebuilding manual which is good reading just so you are familar with the th400..
obviously cooling is an issue so a deep pan, extra coolers, and external filters to keep stuff clean are mandatory for the 502... ( I used the stock cooler, a 30k gvw external cooler, and a spin on quart filters, and a deep aluminum pan on my 454 tow rig) everything came from summit... cost about 300 IIRC... for the 30k gvw it was so big that i had to remove my secondary hood latch to get it to fit nicely behind the grill ( I now have hood pins)
th400s are bulletproof when built right... I dont subscribe to the big names but find someone who you can trust....
the members in your area should be of help.... most trannies come with a one year warranty
hope this helps a little
cam