The cranks are not the "same". You can interchange them with some caveats. The convertor register is a different diameter, so, you can put the 318 crank into the 273 if you use a reducer bushing for automatic applications, and you can put a 273 crank in a poly 318 application if you machine the crank register to accept the 727 converter button. Manual trans isn't an issue unless you're going from auto to manual on the swap. Then you need to check to see if the pilot hole got the final machining for the bushing, or, you'll need to use the magnum bearing or make a custom bushing as the case may be. Also, the crank swaps should require a rebalance due to the difference in piston weights. This also only applies to the '62-7 polys, as the '61 and older had an extended 8 bolt crank flange.
