A list of some tools that will make it easier, but not absolutely needed

A 3/8x16 slide hammer to screw into the front pump to remove. Most pumps you can pop out from inside, but 904s set the pump in real deep, so sometimes it can be hard to pop it from inside.
Something to compress the spring assy on the front drum.
Snap ring(flat) pliars
Retaining ring(round) pliars
Bushing drivers or a bushing cutting chisel to remove any worn bushings. You can press new bushings in with a socket or similiar
A 904 is very basic to build. Leave the low spring and roller assy in the case. Do not remove it unless it is bad
Unless you are using a Shift Kit, build it back to the same specs as OE. Do not listen to some who say tighten this, or loosen that. This trans has been around for almost 50 years and has worked well,even stock!