Some flywheels are drilled and threaded to use both a 10" or a 11" clutch. Generally V-8 trucks used an 11" clutch on an original application. However, many things could have been changed over the years. Be sure to match up the new assembly with the existing components and the flywheel before you dispose of the old parts.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine