I put a new trans mount in my 73 when I rebuilt the drive train, 4 speed trans, strong 383 engine, there seemed to be few choices. I went with the most common one, Anchor, 2512 or 2525 was the part number regardless of brand. Going through the gears I could here something thumping under the car. Came to the conclusion the trans was banging around in the crap trans mount. Yesterday I put an Energy Suspensions, 5.1101R, Poly mount. It uses the existing steel mount, must remove the old rubber and press in the poly isolators. What a huge difference. I was leery of the poly causing harshness and vibration, but it is barely noticeable. The shifts are much smoother since the tail of the trans is staying in place. It's a little more work to install the poly mount. In my opinion it is the best choice given the less than poor quality of the available rubber mounts.