Great advice madmuz, will be chasing threads on this replacement block and your advice on the tap to use to excellent. Sadly as I toiled away cleaning I noticed a few of the lifters are worn through the finish, and peering at the camshaft there is quite a bit of wear on it. The good news is the cam, lifters and rockers are in much better shape on the broken engine so I will stop trying to clean the cooked stuff and use the valve gear from the other motor.