Try Spectrum Color for Gel Coat repair paste. I've used their products with very good success. It'll be hard to get a good match after all the fading but it should still be close. Powder coating is pretty cheap to do around here and will give you a better finish. You should be able to get the windshield off then take it in the house to prep it for the powder coater.
I had a 76 Sea Ray in similar condition and basically refinished all the parts I could get in the house over the winter then finished the rest of the boat as the weather got better in the spring. You'd be amazed what you can take apart and get in your basement when you really want to work on something.