"Also may have our canopy problem sussed. Have found two ex Macchi jet trainer canopies for sale (for charity no less!) at $100 each. Hope they fit! (Anyone know the best way to polish out scratches?)"
Are the canopies acrylic (plexiglass is one brand name for the material ) or polycarbonate (lexan is one brand name for the material ) ? You can use progressively finer sandpaper followed by buffing compound to remove the scratches. You should get some scrap material & experiment with that first. Some buffing compounds *might* react unfavorably with the plastic.
You need to be careful if the scratch is fairly deep, like if you can catch a fingernail in it. Because by the time you get the scratch out, you might have a bifocal canopy. The deeper the scratch the larger area you'd need to san & buff to minimize the distortion.
Some aircraft windshields are multi-layer & have layers of glass, plastic, & sometimes tempered glass. IF the canopies are like that, you're probably out of luck, especially if the outer (scratched ) layer is glass, & almost certainly if it's tempered glass. The glass would take a LOT LONGER time to get a scratch out than plastic, and the tempered glass might just let go. Tempered glass doesn't like to have much if any machining done to it after it's installed.
FWIW I used to be in the glass & mirror business and have dealt with acrylic, polycarbonate, glass & tempered glass.
HTH
roy