62 Dodge D500 New Starter Wiring

1) Clutch has rusted to the pressure plate and/or flywheel. Seen this before and it only needs to stick in one spot. I can't be sure from what you say if the 2 sides of the clutch disc are free from the pressure plate and flywheel, or are stuck to them and the 2 opposite friction discs are just spreading apart.
2) Pilot on the end of the input shaft has rusted/corroded into the pilot bushing/bearing in the end of the crankshaft.
3) Input shaft rusted to mainshaft inside the trannie; did it get water in the trannie? Has it been drained to see?

Your only chance to free this is to hold in the clutch pedal, and have someone tap on the side of the clutch disc, rotate the engine (engage starter for a moment with hands out!) tap it again, and so on over and over. The idea is to make sure the disc is free from the pressure plate and flywheel. Not sure if that will do anything for the pilot bushing; you can just try.

I can't think of a good way to work some lube up into the pilot hole without contaminating the disc. So you may just have to pull it and clean it up.