71 Dart 727 w/suregrip having weird issue

Wheels/tires are good. After toying with the car for a little bit, a couple of the techs there suggested maybe main bearings are wearing out? Since I can get it to vibrate while moving and while in park it has to be something that is still moving when the car is sitting still. IE engine/converter, etc. To test the converter they had me hold the brake and attempt to power brake it but without going as far as to let the wheels break loose. I guess they were looking for the car to vibrate badly under heavy load, which it did not. Which brings my brain back to the engine itself. Not giving up hope, the car hasn't broken me yet.

Also noted oil pressure readings at different intervals. While idle it sits around 25. WOT holds steady at 65ish, no loss of pressure. No knocking during cold startups either.