273 dilemma

The Hot Rod Magazine article on the 273 when it was first introduced says the 273 pistons (or pins, can't remember) are heavier so that the 273 piston/pin weighed the same as the 318 poly piston/pin so that the 318 rotating assembly did not need to be rebalanced for the 273 pistons.

Which reminds me - the 273 forged cranks (at least in 64-65) were the same as the 318 poly cranks. So one of them would work, too.

Someone correct me if I'm wrong, but I seem to recall that the 340 had heavier pistons and rods than the 318, and its crank had larger counterweights, too. Same stroke for 273, 318 and 340, but the 340 crank is not interchangeable without rebalancing.

Of course, one really should have an engine balanced anyway.