Changing Heads

Are you saying that the lower intake manifold is still bolted on? Yes, I guess you could do it with the lower still on, but not a good idea. You would have to remove both heads and the intake as one piece. I would imagine the intake could suffer some major damage.

If you do in fact have the lower intake off, and all the head bolts out of the head, they can be a little stubborn to remove without a little help from a pry bar. All those years of heat cycles will glue themselves to the gaskets. Make sure you have all the bolts out, and exhaust loose, then gently try a pry bar. The heads should come off with a little effort.

Joe

I wouldn't be worried about the block itself. I'd be worried about bearings. Coolant and oil makes an almost gritty-like substance that eats away at bearings, such as main bearings, rod bearings, and cam bearings. But if it wasn't run for too long with coolant in the oil, you should be okay.