That's sort of what I was getting at so cost dependant why not just buy a 200 block as I can imagine there a lot cheaper than a gen 500 block?

Why not ask the tuner who is going to be building the motor what they would suggest? Not a dig but through past experience picking someone reputable and using them from start to finish normally saves a lot of time and hassle along with lots of money even if it looks more expensive in the first place