I just want to toss some thoughts out here and see what happens. I love your design and I am wondering if you have thought about a few things.
1. If your drive shaft is spinning and your drive wheel has a bearing in it, what makes the belt go round ? I am picturing a bearing spinning inside a drive wheel that doesn't move. Doesn't the wheel have to be fastened to the shaft ?
2. Your tubing looks beefy enough for sure but if it's not a tight enough fit will the contact wheel vibrate or worse yet move under the pressure of grinding? I am sure the pressure of the locking bolt will hold it from moving side to side but what about up and down ?
3. The gas shock sounds like a great idea however I am wondering how long a belt will last before it slaps you in the face at 35lbs. of pressure. I would think 5lbs would be more than enough. Some of which may be reduced or increased depending on where you mount the shock. (Think leverage here).
And finally. It looks like your 3" grinder is hanging by the wheel pushed into a crack on your bench? I had one one those fly apart and stick in my chin bone once because it was cracked and I didn't know it. They crack real easy so be careful with that if what I am seeing is what I am seeing. If I drop one of those onto the work bench nowadays, I don't even risk it, it goes in the trash. (Yes, I was wearing a face shield but looking down and then up, raised it enough to expose my chin.)