My car shakes a lot while im driving im pretty positive its not the motor mounts i have a 1970 cutlass supreme
Mud in the tires? haha. Does the steering wheel shake, or the whole car? Have your wheels and tires checked for balance. Check your drive line for balancing weights that may have fallen off and inspect the u-joints. They could be worn and wobbling giving it the out of balance effect. Just a few things that come to mind..
Tie rod end and bad ball joints as well as other front end stuff could also be a possibility.