5 friction/clutch clearance issue in a 904

I set mine up dry....with 5 disc and steels...put the pressure plate on it and flat snap ring..and...measure the clearance...I had to take the pressure plate to match shop and had .020 ground off it as it is case hardened steel as i wanted .070 clearance....done 4 904 like that ..guy charged 25 bucks to machine...as he grinds both sides...give nice clean flat surfaces...