This is for 340 builders

The 340 has a larger bore than the 318 so using 318 pistons is not an option, you`ll have to use 340 pistons. The 340 has a heavier rod, the 273 and 318 used a lighter rod. It may be possible to use a 318 crank but with larger/heavier (340) pistons you would have to add weight to the crank to re-balance it, not cheap. In all it`s not really feesible.