I read in the past an article that discussed problems with GM motor mounts, and that resulted in a very large recall.
The mounts were breaking due to over torquing the mount. When this happened, the engine on the drivers side lifted up in the air enough to 1) bind up the throttle linkage and not allow the carburator to stop feeding fuel to the engine and 2) in the case of automatic transmissions, would actually cause the transmission shift linkage to permanently shift one slot, resulting in Park being Reverse. This was bad!
The fix was the redesigned motor mount that is called the locking motor mount.
Here is a photo of the standard mount (actually, it is shown upside down).
It has 3 bolts that fasten it to the engine block and one bolt that passes throughthe mount, then through the frame, then back through the mount which links the engine to the frame. If the rubber breaks, nothing is there to prevent the engine from lifting up in the air.
Here is a photo of the locking mount (again, shown upside down).
Note the T shaped pawl on the far side of the mount. It is molded to the part of the mount that is bolted to the engine block. Remembering the mount is being shown upside down, if the rubber breaks, the engine can only rise up about 3/8" before the pawl stops it from rising any farther by hitting the remaining part of the mount that is fastened to the frame.
On a side note, during the recall, GM never replaced all the existing mounts with the locking mount, it wrapped a small cable around the exhaust manifold and attached it to the bolt that linked the motor mount to the frame. Why? Beause the cable cost $1.00 and the mount cost $20.00!
Another side note, this modification was not done on Corvette, as there were no instances reported of the throttle linkages binding up, maybe due to the design of the Corvette linkage. I would still consider installing this mount if it is available. It's about $10.00 more than the origional design.