Wayne - thanks for digging those ISO-mounts out and posting the pics. The original one, shown in the center of your pic, doesn't look that bad to me. It's a bit dirty but I think you can just wipe that off. As long as the rubber isn't real "squishy" I'd re-use it myself. And the stem or stem washer on the left in your pic looks real good to me. Many I've removed were all chewed up at the top, which I think happens when the rubber gets soft and the torque of the engine bangs the stem tops against each other.
Matt G - good point about the snubbers, sure makes sense and almost certainly you are correct (as I said, I'm not an engineer). When you tension the PTO to mowing deck belt, or even more so, the PTO to snow thrower belt, it's going to pull the engine down against the snubbers (and squeeze the ISO-mounts a bit) so I can see it's very very important to have the snubbers installed on the ISO-bars, and pay close attention to the "gap" between the snubber and the frame, which is mentioned in the Service manual. Thanks again.
Hydro Harry
Old Cubs Never Die