differences in 904's?

The clutch pack snap ring is selective so is it possible you mixed up the front and rear clutch pack snap rings? The clutch discs are also a different thickness for the front and rear. The rears are thinner. Clearance on the rear clutch pack is spec'd at .032-.055 according to my factory service manual.

I've noticed most overhaul kits only come with 4 discs per clutch pack. I even got one once that only had 3 discs. Luckily NAPA still sold them individually so I was able to get it finished on time.