[BR3W CITY]

My guess is it would only have to contact one side, even for a moment so score the DS all the way around, considering the speed at which it rotates (would act like a lathe). Have you checked the trans mount again? I know you said its "a good one" but is it STILL good or has it suffered damage? BBC on stock motor mounts can move a good bit...bbc+stock mounts +chassis flex and I could see it happening.