At the bottom of the window guide at the latch area, inside and low, there is a bracket spot welded to the guide. In order to remove the rear guide, spot welds need to be drilled so it can be taken out and modified. That little bracket needs to be removed for more room. Ill see if I can find a pic.
Post number 219 (up above)shows the rear window guide in its recessed slot, then welded into place.
I hope this helps
Dne'