OK, here goes for SFT:
'70s Poly doesn't compute, the last Poly was something like 1968 in Canada, 1967 here in the States.

For the unschooled, newbies, etc:

All 273s are neutral balanced even though their pistons weighed much less than 318 pistons, and the 318 pistons and rods were used in the 273. Chrysler engineers made up the weight different with special heavy wall pins for the 273s.

All 318s, from the early A Poly to the post-LA 5.2 Mag, are neutral balanced. Forged crank 340s are neutral balanced.

Cast crank 340s have their own factory imbalance and don't interchange with anything.

The cast crank 383s, 400s and 440s all used the same factory imbalance and can be interchanged even though they have the warning cast in to "use with cast crank XXX engine only".

440 engines with the 908 rods used a different amount of factory imbalance and have their own specific damper, although the issue is confused because later on some heavy rod engines used neutral balance dampers, IIRC.

The 360s had a much different amount of factory imbalance and are useful only on 360s.

5.9 Mags have their own imbalance and it's less than the LA 360. I expect that dampers should not interchange between the two. 5.9 Mags with automatic transmissions used an imbalanced flexplate and neutral balanced converter. This makes life easier.

R.

PS: I don't think the damper in the photo has an unusual amount of drilling on it. The amount of metal lost is much less than that for a 360, for example. I have seen that drilling on many 318s.