Stop concerning yourself with the transmission. You're not buying a transmission.
Are you trying to do this on NAPA's website? I tried; it's dreadful. Still, if you go to the top of the page and enter the vehicle and engine, then search "clutch" it's going to give a bunch of automatic garbage. Among them you'll find two manual options: 9.25" and 10.0". 9.25" is the stock replacement; the 10" is a size upgrade (trucks used a 10" disc on a 122-tooth flywheel).
It doesn't show any manual transmission options for lookup that I could find. No 10.5" option is shown because that size will not physically fit on the flywheel.
If you need a clutch for a '72 Duster with a 198, look it up for that. Stop trying to force the issue of what transmission it fits; as I said above they all use the same clutch and its attendant parts.
