Ken.....Yep, the original block. Has been "validated" to my satisfaction. I have owned the car since 1972, am the second owner, and I know for sure it came from my car......I'm the one who removed it. I have talked to the original owner, he lives only about a mile away from where I live, and he says the engine was never touched when he owned the car.
BTW....we have discussed the 50 difference in the VIN's before over on TC.