904 front drum q.

Sounds like you adding an extra clutch in your direct drum. While you can grind it down to .078, it will be to thin and cost to much. The plate will warp when it gets hot in the trans.
When I did my 904, I measured the clearances and gave the numbers to the machinest and he step cut the plate for snap ring clearance. The plate is still mostly .216 thick and I have .075 clearance between the pressure plate and clutch. I also used the thinest snap ring.