NEVER, EVER run a solid trans mount. Chassis flex will break the trans. Just because a Chevelle is a full frame car does NOT mean it doesn't flex. The 71 Chevelle I used to have was inconsistent until I welded a roll bar to the frame. BIG DIFFERENCE. That gave me a clue as to how much it was flexing. Put at least a bar in the car, cage is better. ASAP. But still no solid trans mount.