Belt rubbing
Looking at your pictures, it looks like the belt isn't perpendicular to the table. It could be just because the way the picture was taken, but it led me to do some research. I measured my 66 from the center of the belt to the back of the arm, just sighting with a ruler, at 3/4 inch. I then hung a long needle from the center of the belt to the base, ( like a plum bob) and it is about 3/8 inch from the edge of the base. Is this true of yours?
I did this just wondering if somehow the hand wheel is, or could be, spaced out from the machine in a way that made the belt rub. Just a thought... And without taking the screws loose, is there enough play in the lift assist to "pry" it towards the base of the machine? I have one of those on my 15-91, but it has no side to side movement. In your picture, it looks like there's a space between the lift assist arm and the base of the machine. Is this enough to allow the belt to rub?
I was just musing over your problem.. TV is boring.