Robert,
Get some "welding" solvent (glue) for those cracks. The stuff is thin like solvent, and it evaporates very fast. It essentially fuses the plastic together. If you have a plastics fabrication shop in your town, go to them and ask to purchase a squeeze bottle of it. Gonna cost about 8 bucks. The bottle holds about an ounce of the stuff, and it has a needle-like applicator on it. Clean the cracked area best as you can with dish soap and spray it out with water. Let the crack completly dry out by forgetting about the windshield for a day or so. Then take the plexi glue and weld the crack. The glue will be drawn into the crack by surface tension of the solvent. Place the needle tip at the end of the crack and drag it along the length of the crack while dispensing just enough glue to fill it. Don't be too stingy with the glue - but don't get carried away, either. If there are any drips or runs, immediately wipe them away with a cloth rag. Do not use a paper towel. Use a single wiping motion in one direction. Do not rub. It is a good idea to do this from both the front and back of the windshield, to be sure the crack is completely wetted out. If you can tilt the plexi to get the help of Newton's Law, do it. Once the cracks are welded, leave it alone for a day. Come back and use light rubbinbg compound or plexi restorer & the cracks will hardly be noticeable. Don't drill "crack stopping")holes at the end of the cracks - that old trick has never worked for me or anyone that I know who has tried it. You can make a replacement windshield out of Lexan - it can be cold bent. As for the top edge molding - I have been trying to find a source of the correct material for some time now. So far, the best bet I have found is to find an old trim from another doner boat with a similar windshield.