try some IPA on the window, that can be very good at softening glue.

Measurement wise do not take them as gospel as you may find you need to tweak things slightly the joys of a fiberglass car.

I used ethanol, because we have it as a perfume base, and it does seem to work with quite a bit of rubbing with a soft rag we now have doors assembled and engine cover mesh grills fitted in the house and I refitted the front section back onto the chassis on Sunday afternoon, I was attempting to get the rear plexiglass window in but failed as soon as I got to the halfway into the seal rubber stage, when it popped out at the corner, I have long ago fitted screens, even in my old Cox after breaking one, but never one with such tight radius corners, advice is welcome if you have done it
John

After another frustrating Sunday morning failure to fit the rear screen with the smallest section (and corner radius) of sealing rubber from Seals Direct, plan B has been executed, as I had to buy a sheet of Polycarb material at least I have plenty left over to make an oversized rear screen with an additional 1' added all around, out with the jig saw, get cutting then off to the kitchen screen in hand with a hot air gun and using my biggest cooking pot, which was about right compared to the original screen, to form the end radius after heating the sheet, if I can find here I will use plastic number plate screws or if that fails pop rivets.
John

Nigeria is a funny old place, from almost running into about 40 camels being walked along the main road into Kano at 5.20 this morning while still dark, suspect they were not kosher, why would you walk them in in the dark at that time, stolen camel steak for Xmas i wonder??
PU sealant seams to be almost not available here, window installers use silicon sealer?? I did find and buy a tube of German made but branded Visa Petroleum PU 6988 (Nigerian Company) on sale to test, but testing was delayed as no nozzle supplied and bigger than the normal silicon sealer nozzles, so Sunday morning was spent disconnecting all the engine/subframe attachments prior to dropping it down, all I can say there is a lot more bits attached than in my old car!!
John