Did you try draining the oil(if it was stored that way)and pouring fresh oil through the engine a couple of times?

If it's been stored since '72 without being turned over sometimes all it takes to loosen the bearings is some fresh oil to coat.

You may also need to get a LOOONNNNGGG cheater bar to get more leverage on it. 3 foot or longer.

I've got a bone stock Flathead 6(don't yet know the size, sorry)in my Savoy. I'm looking at much the same motor and issues.