I have done several 6 to V-8 conversions on TF trucks and used the original throughout arm regardless of what size clutch (11" or 10") was used. I would personally use an 11" clutch with that vehicle/engine/transmission.You can try to get a measurement on the pressure plate to be sure. It's likely that being it is a larger truck it would have an 11" clutch. Then you could buy a flywheel to accept an 11" clutch. However, you can't take anything for fact for something that has been around for 60 years and has been worked on by numerous people.
I'm not going to comment about re-drilling a flywheel.
I would also use a new clutch, you only want to do this once,
Fred
You still need a pilot bushing, they are not installed on engines that came with automatic transmissions.
