The pad with the interlocking tabs is designed to be on the driver side. They are a "catch" if the rubber fails to prevent the engine from lifting on the LH side due to high torque. I believe that pad originally went on trucks so the frame mount position may have been set up for that thicker pad. (Let's hear from some of the experts on here that may know which truck/engine, etc!) The tabs function somewhat like a built-in torque strap if you believe they could really hold back the engine.
