Crank

One difference between early 273 cranks and 340 cranks is that the early 273's had a smaller register for the converter snout, so a later model converter won't fit. I found out the hard way a long time ago. It can be machined out. But you would still have to rebalance the crank to the rest of the assembly either way.

I don't recall what year they went with the bigger register and I can't tell by the pics. But it would be a good idea to measure it and post the numbers. Someone else may know the specifics.