My 46 b has the same problem, I just wrapped the shaft with thin shim stock and drove the drive on to confirm the shim stock to the splines and it's been running fine for years.
I'm guessing you know that the spline on your crankshaft is tapered and the internal spline in the clutch plate is a matching taper. So when the the two are together they taper lock.
Enjoying this! I'm working on an old 620 that is the same rusty. Had to replace the coupling on the oil pump shaft, got it running good after a carb rebuild and gas tank cleaning, but an awful noise is now going on around the pulley/clutch area, so I'm gonna take that apart. Check my channel too! I'm in Indiana. Keep up the great work!
