Update: I was able to drive the pin that connects the winding arm to the crank. I used a pen and, with intense force, I pushed the pin while rocking the arm far enough until I could pluck it out with needle nose pliers. I was really nervous about using so much force, but I guess Yashicas need tough love.
Unfortunately, I found out that I *really* had no business dealing with the crank assembly. I initially wanted to go under there because the winder would jam in mid motion, but the problem somehow resolved itself when I reattached the lens board back on. The other thing that I realized is that I never considered how important having a real roll of film in the camera would be to the whole operation of the camera. A fresh roll of film coming in would drive that film counter wheel, and a closed back would engage that gear onto the counter, creating that correct "ratcheting back to the original position" that has been elusive to me.
So that winding forward indefinitely problem was me being an idiot and not thinking things through. Though I doubt the person who had this before was thinking it through either - this camera definitely had more than one diy repair in its past.
However, my question about the washers between the lensboard (lens and shutter assembly) and focusing rail still stands. The lens board was screwed onto the rails with four screws, two on the top and two on the bottom. When I took the board off, there were two washers between the board (one on each side) and the rail, and none on the bottom two. Are there supposed to be four washers all around? Or are two on the top actually correct?