I'm gonna guess here, and say that endurance racing with an automatic is something even the guys at Ford Racing don't have much experience with. 99% of race automatics are used in drag racing, where it's all over in 12 seconds.
Further guesswork, heat comes from slippage. You're running at or near full throttle all the time and the converter doesn't lock up in that situation. And the converter puts a lot of heat into the system. Maybe a toggle switch (or a tune?) can force lockup? Which may kill throttle response and acceleration, but would let the trans live.
Might be time to think about a manual swap.
As for pans, my Trick Flow pan holds one quart extra:
It's just an RCH lower than the crossmember, and still above the exhaust. You should be able to use a +2 qt pan without bottoming out, but I don't know how much it will really help.
1988 CVLX Formal Roof (Love Boat) POTM July 2019 & Aug 2020, 56K
E-code lights w/ relays, LEDs w/ switchbacks, 15x8 Ansen slots w/ 255/60 BFG's, Kenwood stereo, various hacks.