I bought a sonic gauge, I scanned both the 400 and the original to my car 383. (6-26-68) like was stated above, both blocks are all over the place. I am not looking to build max effort strokers though, so i'll do the usual band aids to help the motors live.

Ultra sonic thickness gauges are addictive, I scanned everything in sight while learning to use it. scanned my Cat, he's good for an overbore, lol.......

Thanks again for the info.