As a manufacturer of solid body bushings I will try to help .
First let's clear up why the factory use rubber bushings. Simple, that's just the way they did it, a left over vestige of the full frame cars, the frames were simply bolted to a frame and isolated with rubber, it also dealt with the misalignments of the days.
Those that say 1-2nd gens used rubber bushings as an isolation to nhv is not the only reason again "it's just the way they did it"
Understand that GM did not isolate the frame from the body on the Chevy2/Nova, it was solidly bolted.
Modern cars have the front frame welded to the body.
if you install frame connectors you must use solid body bushings, and those that want to make any argument realize that the frame connectors will make a solid connection!
Poly body bushings are fine as a stock replacement for a cruiser, but they are not good for hard performance use they can pop out of their place.
I see this on a regular basis about body bushings "squeak", they can't squeak since there is no movement!
Polygrafite is a marketing gimmick.