Just curious, how was the engine-trans supported? Especially with a manual trans. I would say a lot of external forces being applied to this engine to go along with the internal ones. Bob Glidden wouldn't use a engine stand to build his engines because it would stress it differently then the machining was done. He built them vertically setting on the flywheel, but heck, what did he know about engines. One thing I would do on the next block is have it stress relived in an oven since you don't know how many cycles it's been through.