Three motor options

A 360 will need a new engine mount on the passenger side, but no changes to the K member.

The seller of the 340 is dreaming. The missing carb, intake, cam etc. wouldn't bother me, all that is probably going to get replaced anyway. But the missing main caps are a problem, that adds a line bore to the price of your rebuild, and of course you'll have to buy the caps. And then you'd still need new rods too. Plus it kinda sounds like the engine isn't in the best condition, and that could come back and bite you somewhere else in the rebuild.

It'd be cool to get a date correct 340, but the 360 sounds like a way better deal.