I would like to pass on a tip that might save some time and effort for others, as it has me.
When replacing the windshield frame to the body on MGBs, the holes have to be in almost perfect alignment to install the four bolts that hold it in place. This is difficult (especially when the dash is in place) since it has to be done by feel. I have found this is made much easier by substituting the regular bolts with tapered bolts. The holes need only be aligned enough to start the bolt, which will then pull the frame into alignment as it is tightened. Suitable bolts are General Motors # 39986997 or 14011722. These are easily found in wrecking yards holding the hood hinges to the fender of may GM cars of the 1970s.
Addendum September 2007:
You can find these tapered bolts at the New GM Parts web site.
Search for GMC part number 14011722