SSM Super Platter help please

I have the same set up you're describing and it's working very well. It does however, require a little patience anytime I make changes or even move the thing. As I recall you have the new drive belt as well. It takes some trial and error to get the height right but with the mini feet especially you should be able to make it work. The drive has to hit the "land" between the groves on the platter but I don't believe it has to be the exact center. Mine is but it just worked out that way. The mini feet give you quite a bit of flexibility in height adjustment but if needed you can also set them on risers of sufficient thickness. My table sits on a Critical Mass Systems platform with their spacers under the feet. I also had some aluminum spacers made to size to try with materials from McMaster-Carr. The peripheral ring clamp also needs room to spin above the rim drive so it takes a little tweaking.
If I had to guess about your speed issue I would say the contact pressure is too high. It's very important to have the lightest contact pressure that still allows smooth start up. This sounds simple in theory but in pratice can take as much patience as cartridge alignment. When you're at the right pressure, the super platter will continue to spin a couple turns on shut off after the drive is still. This also allows the platter to spin faster( much faster then with the belts in my case) Don't abandon the replacement feet due to height issues. You can work it out. After all this seems in order, I find the drive really needs about 6 hours of run in time at the least for speed stability to settle in. Finnicky to be sure, but when dialed in it's hard to beat.

59.10 right now on 33 1/3. That can change slightly each day depending on what I see on my KAB strobe. I'm not really into 45s currently so I can't tell you on that. At a light enough contact pressure it runs nearly silently and speed stability is now dead on. Initially I noticed an oscillation of the strobe's numbers back and forth. It's hard to move this heavy motor assembly in small enough increments to hit the right pressure but once you do I think it will be obvious. The new more tacky belt allows better grip at a lighter pressure in my opinion. Fractions of a millimeter make a big difference.

Yes, the voltage is at 84. Sorry, forgot to add that.

It's been a while(1 1/2 years or so)but that sounds right to me. I just changed the bearing and as I recall just used one large steel washer. The heavy platter just slid onto the bearing after that(it was pre-greased). It's probably the easiest(along with the mini-feet) of their upgrades to implement and also one of the most worthwhile(along with the rim drive which requires more effort and patience).