The "Throw Away 318"

318 power is a known recipe. We did it all the time. No need for a 340.

1. 318 short block, rebuilt, bored and honed with torque plates
2. pistons in the compression ratio to work with the gas you want to run
3. balance the rotating assy
4. 360 heads, pocket ported, competition valve job, mill flat to get a good seal, gasket match if you want
5. whatever cam and valve springs you want
6. Intake and carb

If all is the same as a 340 except the larger bore, most people will not be able to tell or feel the difference.