engine/trans vibration

The 65 converter (stock) had a smaller diameter nose then the hole in the crank of the later engine. It is possible your converter was built with a large pilot nose. years ago those converters (hybrid) could be obtained, but now are very pricey. If your converter has the small pilot nose, you need an adapter bushing in the end of the crank. You will need to measure the pilot nose of the converter. If it measures 1.81 inches, that's fine. If it measures 1.55 then you need the bushing.
PS: I sell those bushings. If you do need one PM me.