Get a copy of Leo Santucci's book on hot-rodding Chevrolet 6s. I think you will end up going with a 292 high-deck instead of a 230 or 250. The 292 motor mounts are different from the 230/250, but all three of the late model sixes motor mounts are different from the 216.
You might need a custom drive shaft, but those are available in most large cities.
