MeganMills - this is such a helpful write-up! I got a belt installed on my Singer 66 treadle last night (managed to get it with the first belt, though yes, I do have 3 different sets of holes).
I had moments of having it go well, and moments of not so well. I knew about the dead spots (and have identified 2. I'll have to see if dead level is a dead spot for mine as well). Sometimes I can get it going easy, other times I am confused as to which way to push, so this is so helpful reading a thorough description of the actual experience broken down. I wanted to see last night if I could get any stitches (I could). I will be practicing now for a time sans needle and thread, until all of this sinks in and translates to my feet.