Poly- urethane motor mounts"?

I have poly spool mounts on the 340 in my Duster and at the T56 transmission mount, never had an issue with them and engine vibration hasn’t been an issue. The engine mounts have been in my car since the 340 went in, and I was running a poly mount with the 4 speed before the T56. Over 30k miles on the engine mounts so far.