What you overlooked is that those bushings have inside "shoulders" that meet in the middle of the 1-1/8" diameter holes I cut in the motor plate, when the through-bolt is tightened down. Nowhere does the mount or the bolt come in contact with the plate - therefore it is indeed insulated!
If I'd put a pad between the mount and the frame, the through-bolt (and spacer that keeps the frame from crushing) would effectively bypass the isolator and transmit the vibrations directly to the frame rail.
See the article on BBD's Tech Pages if you want the details.
