Pat,
I'd say start with the basics. You know you have a wheel weight which has gone kaflooey -- rebalance that tire (you need to do so anyway) and see if that doesn't fix the problem. It MAY be totally unrelated to the motor mount R and R.

From my reading, and limited experience, vibration problems you can "drive through" (i.e., you can detect a discrete speed when it starts and stops) USUALLY turn out to be tire balance issues.

__________________
Steve
'93 400E