Fluid filled damper for ‘78 440

Yes, those are visibly wider.
I wonder why they used those in cast engines. Any insights?
I dug through my library of big block books, figuring I'd find the answer and they all seem to stop at 1974.

There are references to them being used in trucks and motorhome steel crank engines though.

Googling the question doesn't give any other answers either. I'm really beginning to doubt myself about this...

Somebody here has had to have one apart...