Motor Mounts?

Hello All!
I'm lookin' at a 1991 SC with a 5speed and 110K miles. When I rev the engine in neutral the whole car seems to shake with the speed of the engine. Now I'm new the these year Thunderbirds and I don't know if this is normal or something like the motor mounts.

Yes it could be. If it has the original motor mounts they are probably shot.
You need to get under the car and see if the oil pan is rubbing or sitting on the support underneath it.