Here is my guess:
The crank casting probably suffered from “zinc pest” (as is often true of early 700E castings). One of the things that happens with pest is that the zinc expands. Because the portion of the casting you are trying to remove is located inside a non-expanding metal tube, the zinc is now squeezing the crankpin stud. This is why you are having trouble removing it.
I advise against trying to pull or wiggle the casting off of the stud because you might wind up loosening the stud or perhaps even pulling the stud out of the driver. If you were to do that, repairing the damage correctly would be extremely difficult. (700E crankpin studs are not the same as the postwar 773 studs. You'd need access to the back of the driver in order to secure a 700E stud correctly.)
I suggest that you gently try to break apart the zinc casting. It is likely to be brittle, another well-known side effect of pest. This type of repair is outside my area of expertise, but I think what might work best would be to use a low-speed Dremel tool with a very narrow diameter drill bit, and then drill into the zinc casting just inside the interior edge of the metal tube. Several holes may be needed. Do not drill near the center of the casting or you may damage the crankpin stud. After you have degraded the structural integrity of the casting, especially if you are able to shatter it, the casting should come off pretty easily. Good luck!
