When I did my boat over I bought a fiberglass windshield insert. The inserts are made of glassed over foam and sprayed with gelcoat and they take the shape of the origional windshield. All you do is take out your origional glass and frame, clean everything up reel well, put the insert in and 5200 it. I then had to do some minor glassing and filling around seams. It's easy, and took me total of 2 and 1/2 days. I don't remember who I bought mine from but I would buy from him again. He was back yard builder and his measurements were a little off. I know someone who bought one from Glasstech in Florida and it was perfect and easier to instal then mine.
I really wish the guy that was recommended to me for the fiberglass plug would have called me back because If I had it to do over again I would look for a one piece plug as described before. We did a fiberglass cowel from Richard Bertram and unless you are well versed in expanding and fairing fiberglass parts I would steer clear. The other issue is after you have the exterior looking pretty you are still left with the cosmetic situation inside. The cowel simply fits over the aluminum frame so the view from the inside is....... THE ALUMINUM FRAME!!!!!!!
Even if the plug is twice the money you'll save in the end by taking less time and having a finish both inside and out.
FYI our fix to the aluminum frame inside is to build white vinyl panels on fiberglass backers. This way the inside will at least appear as finished.
Bill Holmes @ Holmsey Co, Inc. in Jupiter has a mold for the two sided cored insert. He told me he could tweak the mold to fit the boat. You give him the inside measurements for the top & bottem corners and he'll push or pull the mold to fit the measurements. Price was $1900,00 fob Jupiter, Fl. 561.746.3476
Good luck,
RussP