What kit(s) to buy for a mild 904 rebuild?

12008C kit from trans star is a good start. Tony - 70AARCuda used a bunch of these in his 904 race builds.

Another that I've bought from before and got good service.

A904 HP Rebuild Kit A998 A999 Master Banner Overhaul Automatic Transmission Dodge Chrysler Jeep

Funny story that one of the mopar trans guys was selling seals... special teflon ones... ordered them and they came in the EXACT same bag with same number on them that I got from a warehouse supplier. Only cost twice as much! LOL
Don't fall for that nonsense. Most everyone gets the same parts you can get from a warehouse supplier.

If you want to add extra fiber to the drum, ask if they can put thin frictions/steels in and buy a couple of the thick steel/fiber. Comes in handy for setting free play.