Call Portland Transmission Warehouse: 503-233-4966, 1016 S.E. Hawthorne Blvd., they're in your back yard. Tell them you've got a 68 904 and they'll get you the right stuff.
As Trailbeast said, get the kit with steel plates, bushings, washers, filter etc. You've got it apart now and no sense in doing a half-assed job .
When I worked in the industry, TRANSGO was the shift kit most commonly used in shops. For a stock application, the Transco (same company as Transgo), small SK-TF shift improver kit will more than suit your needs. In the forward drum look the diaphragm spring over very carefully as they are known to crack, and maybe consider replacing the overrun clutch rollers and springs (AKA the sprag), as the springs can weaken. Replacing both items cheap insurance.
It's apart: DO IT RIGHT "ONCE".
