Hey Jim, I tried to put the rear glass in my '53 useing the same tool you were trying to use with the same result. I then ordered the same orange plastic stick/tool Jockbolter used and it worked great. It took me a while but I got it done.
When you cut your window rubber, remember to cut it long. I cut mine almost 1 1/2 inches too long, then forced it to fit. The rubber will shrink over time.
Also, I put the seam in the window rubber at the bottom of the window, and the seam in the lock bead at the top. I figured that this made for a tighter seam in both and less chance for leaks.
