Looks like after measuring my original '54 3600 4 speed clutch, it measures 10", so anything over that won't work for me in this situation. Probably stay with the 9 3/16 S-10 disc unless I can locate a 10" one. Have not looked yet.
Tried my new P/S pump tonight and it appears to be metric, so probably be sending that back. Getting pretty frustrated with all the inconsistencies. Someday I'll get there...