Wow, it's great to hear all your inputs into my experimentation, I thought I was going to have to "go it alone" , but now it feels a little more like I'm part of an age old riddle that many people are trying to solve. Thanks for the suggestions/comparisons, I appreciate them.
Since the second video, (the dancing one) I have removed the bottom steel plate along with 4 out of 5 of the 5/8" rubber pads in each foot. I also cut off the jaw-like tabs that corralled the 5 rubber layers, as they will no longer be needed with only 1 layer of rubber. I will be trying the single pad attached to each of the 4 corners with no steel base plate beneath it this time because that seemed logical for better traction. I will see how that combo bounces, and then move on to spring experiments, or maybe a combo of the two. I work around large generators and they all seem to use springs as their mounting systems, granted that these are multiple cyllinder engines and have different dynamics than a one lunger. Like you Steve, I am reluctant to pour a giant slab of concrete and plus I would like to house it inside my garage. There must be a way to do this, plus I enjoy the challenge. That stiff frame is the way it came from CMD. That is definately key to working out the vibration issues.
Carlb23 had an intresting setup, rubber then beams then rubber again and not bolted too tight, perhaps all you need is to happen upon a certain combo that works with your weight, rpm, rotating mass, etc. and your all set?...
I keep playing with the idea of a three dimentional steel box welded up solidly with your generator unit bolted ontop of and containing some sort of bladder inside it that you could fill with water to give you a massive (weight) base. it would not be as permenant, and you would still have the large mass to bolt the spring/rubber feet to. Ok, my mind is drifting now...
I will test the rpm to see if it is actually 1000 also...