Thanks RRR. For the record I’m going with the 318 crank only because the 340 crank needs grinding and then I’d have buy bearings, which is going to take a while, plus more $... Regardless I will balance the assembly so it’s all done right.
Just make sure you do, because that 318 crank is dedicated internally balanced. Now......here's a twist. Take them a 318 balancer. Let them check it with that. It might be that it will cost a lot less that way, since the 318 crank was internally balanced. With the 318 internal balancer, it should take less Mallory metal and be much cheaper to balance. I would also recommend a quality balancer too. Having it balanced with the 340 external balancer would get costly, since the crank is internally balanced and would likely require a lot more Mallory metal. Dat chit ain't cheap.