will they work?

Whats the problem with the heads that are on the 340 now? They are most likely 915s, which are a very good (if not the best) head for the 340. They will already have 1.88/1.60 or 2.02/1.60 valves already, plus larger runners for more volume flow. Much better for the 340 than the 302s, in my opinion, Mike