Need 904 assembly help!

Can't comment if you got all the parts in since I didn't see it go together, but basically the small thrust washer mostly sets the input shaft end play. As for the gearsets, there should be a snap ring that goes on the output shaft inside the case, in a grove in the shaft, to the hold the gearsets in during assembly, before that thrust washer and forward clutch go in. Nothing really big or robust holds the output shaft and gearsets together, so it may be correct. Study the exploded views to see where everything goes if needed. I don't currently have a 904 apart to get pictures, just a 727.