Somebody besides me will come up against the flywheel/clutch/bell housing issue when switching to a 12V starter or 6-bolt clutch for AD trucks so...
I've done a little research on flywheel part numbers. For trucks there was a bell housing change in '54 and flywheels changed also. Flywheels again changed in 55 from 139-tooth to 168 tooth to accommodate 12V starter. I think the 54 flywheel is unique for HD clutches.
42-53 - 3/4 and 1-tons and apparently some half-tons with heavy-duty clutch - part 3705387 (heavy-duty 9-bolt clutch)
54 and later trucks got a new bell housing, casting number 3835201.
54 Flywheel - part no. 3703579 for heavy-duty clutch.
54 Flywheel for standard-duty clutch - part no. 3704831, appears to include passenger cars.
55-62 235 & 261 w/10-inch clutch - part no. 3705409
55-62 235 & 261 w/11-inch clutch - part no. 3789730
GreyGhost's flywheel part no. 3705410 I'm guessing is 55-62 with 12-in clutch but I don't have the parts book for medium & heavy-duty trucks of that era, only up to C-30. Perhaps he can confirm if it is drilled for 12" clutch.
54-59 list both 10"and 11" diaphragm clutches, so apparently the bell housing change and clutch change from 9 to 6 bolts came in 54.
60-69 lists coil-spring, 11" clutch for 235, 261, and 230 engines.
