The mysteries behind engine balancing?

The 273 2 bbl and 273 4 bbl (hipo) had different piston pin weights to compensate for the 39 gram difference in the 2bbl and 4bbl pistons. The extra 24 grams going from the 273 4 bbl piston to the 318 piston was also compensated by lowering the pin weight.

Engine: Rod+pin+piston=total
273 2 bbl: 726+220+530=1476 gr
273 4 bbl: 726+184+569=1479 gr
318: 726+154+592=1472 gr

So the later 273 and early 318 cranks could be the same. Not sure if the later 318's changed weights or not.

The 340 total weight shot up to 1631 grams, so not the same crank, even though it will fit in place of the 318 or 273 and vice versa.