A-Body Round #2- My '76 Scamp restore...

I would use transmission fluid. put a cup or more in and let it sit a few days. Then a few taps with a block of wood and a hammer and it might just free up. Doesn't actually look that bad.

I have a 51 and a 49 international truck and both were stuck. Thats what I used to free them up. Filled each cylinder and let it sit during the 25 hour drive from my brothers to home. Once I got home the 49 was already free and the 51 I was able to turn on the flywheel.