318 to 340

FWIW, I just measured a standard bored 273 block that had pretty nice walls. If it was bored .065" on all walls, it would end up at .120" minimum on any thrust face, and .115" minimum on any front or rear wall. It might work out for just driving around if you found a 318 block with such even walls. But as said, there are better ways to get to what is desired.