What's the difference in diamter between what came out and what's going in? On a 126 there are different mounts for left and right. The originals and replacements are marked left and right. I can't tell the difference. Each one seems symmetric about the vertical axis. Maybe you can check part numbers.

I replaced the ones on the SDL last week. They went about 10% of the way in by hand and seated very easily with me turning by hand the yoke on a Japanese car scissors jack. This was with a light dusting of Silglyd.

If getting the mounts in is this much work, wait until you have to get those 50 caliber bolts back in place.

Sixto
91 300SE
87 300SDL
83 300SD