63 SB motor mount opinion

Yes, it's a safety item... if the rubber in the new mount deteriorates and breaks, the engine is limited in travel. With the old mounts, if the rubber separated, the engine was free to move/rock excessively under torque load during acceleration; there apparently were incidents where the engine shifted and jammed the throttle linkage at full open. The downside, if I'm not mistaken, is that the new mounts may be larger and thereby interfere with the fitting of ignition wire shields and the normal routing of the spark plug wires.