All this does is move the freewheel over a few millimeters and possibly allowing the derailleur to properly engage that last cog. It is just a possible solution to his problem. I had the same problem with an old PR10 that I was mounting a threaded derailleur on. Even when I was using a derailleur with the full range to engage the last cog I ran the risk of the derailleur catching the spokes. It was just too close. Rather then changing out the derailleur, hub, dish, freewheel, or bending the frame, I just threw in a spacer. And it worked! Latter I moved the spacer to the inside of my freewheel as I described in my first post. I am not a bike mechanic and just found the spacer provided a simple solution. In all my frustration I did not try new bar tape. But if I had thought of it I would have...

Vintage Campy-Rally Deraileur Mounting