What do I need for my 904 rebuild?

Fishy68 (Tracy) can help you with which kit and where from I think.
There is a full soft parts rebuild kit that comes with pretty much everything for a basic rebuild, or a master kit with bushings included.
A stock 904 with the shift kit should be plenty for a mild 318 and last a long time.
And as RRR says, rigid bands are a nice addition.