HI Dan,
Well, you've hit on one of the two most controversial topics on this entire site..... trannies, TC's, valve bodies have resulted in open warfare, name calling, and spit balling... .
Having said that, I encourage you to look around, make some calls.
You should speak with the major suppliers, and one in particular.
Remember, I have not had personal experience with any maker aside from stock (DC) and DTT. On the up side, they will treat you like a family member. They'll simply info/support you to death, walk you thru procedures while you laying under the truck too.
This is all my personal opinion/experience and is NOT based on any secret or inside information.
If you intend to do a full rebuild on the transmission, I'd strongly recommend you talk to Bill K. Especially if your dad is going to tow.
DTT's convertors are pretty much the top end in terms of fluid coupling. Again, since you're doing a full rebuild he can possibly recommend some "badly needed" components to incease life expectancy as well as performance.
The DTT convertor (89% or 91%), one of their "towing valve bodies", some seals, apply lever, accumulator parts, are some of the things that come to mind.
Now there are lots of aftermarket TC's/valve bodies out there and you'll find the one that suits you, but since our trucks do not use lockup TC's you'll need the best in fluid coupling... that's Bill at DTT. He'll talk you thru the mods, help while your laying under the truck and it's all part of DTT's attitude toward customer(s) service.
I think his equipment has been the best single modification I have made to my truck.
Disclaimer:
This is all my personal opinion and should be taken in that context. It does not necessarily reflect the opinion or endorsement of or by the TDR. I am neither supported or sponsored by DTT.