Beefing Up 904

I know this has been discussed often here on FABO, but I also know tech, means and methods and parts selection are updated regularly, so here goes…
I’m replacing my original 318 with a 340, and while it’s out, I’m taking my stock 904 to a shop for rebuild/strength updates.
Any suggestions, advice and help you guys could offer would be greatly appreciated, since I know next to nothing about automatics and they’ve always been something of a black art to me.
Whatever brands, parts, advantages, disadvantages and pitfalls recommended will be studied, researched, pored over and implemented with great care, as I only want to do this once.

Thanks in advance to all the FABO tranny gurus and everyone else on this great forum for all the help and advice in this project!