There's tons of variables that go into Engine harmonics. Compression, camshaft lift, camshaft duration, connecting rod length, crankshaft deflection, etc...
If you want to get more in depth you can go right down the driveline; transmission(s), driveshaft, rearend, radial tires. All are contributing factors to the overall harmonics of a vehicle.
It seems to me, the engineers just picked a narrow range of variables to work with and then picked the best dampener to work in that range. Why else would you have the same dampener on a 283, 307, and 327?
I too have ran boats that have no dampener at all. For you farmers, go out and try to find the dampener on that Oliver. It isn't going to have one.
Even though the dampener Jerry picked, isn't technically the right one. At least he has one. I'm sure it's better than the 60 year old one that came off the engine, and probably alot better than a "remanufactured" Chinese one.
