sb difference fuel consumption

You can grind the crank mains, no problem. (and it's inexpensive). It's the custom pistons that you need for a .030 over 340 block, that will cost a lot of coin. If the 340 block can be cleaned up with only .020" removed then standard off the shelf .060" over 360 pistons will work and not break the bank.

also,

I would go with Rumblefish's sugestion of the XE262H cam. Anything larger and the mileage will suffer.