Thanks for the info on the heads. I talked to my machinist/engine builder today. He said the cylinder walls are only .160"-.180" thick on a standard block and a quick check. I'm leaning towards using Hardblok, but sleeving a block is a more expensive option. I found some Melling 1/8" sleeves that would bring the 318 bore (3.91") down to the 3.66" range. My machinist suggested getting Darton or someone to make some extra thick sleeves and put them in a 340 block. Sounds like a very expensive way to go and this is intended to be a budget build.