The 1970's through the 1980's motorcycle fairings and trunks were made of ABS Plastic -- same as Plumber's Pipe Glue. The Pipe Glue is really ABS Plastic dissolved in Acetone: the Acetone evaporates, leaving behind ABS Plastic. I made repairs to around four different vintage fairings and trunks, using Plumber's Pipe Glue; Craig Vetter sold a Hotcha Repair Kit ($$$), but I just used Pipe Glue, at a small fraction of the cost, and it worked flawlessly -- some of my repairs are 8+ years old and still strong and functioning. I sealed the holes with masking tape: after the Glue cured, I removed the tape, which left behind a mildly rough texture. In this case, based on the photo, above, I would reinforce the metal threaded receivers, by adding additional ABS Glue around the, to build up the fixtures, giving them more strength.
The Pipe Glue is always black, by the way, but on the underside of the hood, who cares? It needs to work; beauty is in the eye of the tractor's owner, and
functional is the most beautiful thing, to me.
I would suggest giving Plumber's Pipe Glue a try, before you go with Fiberglass resin. You will know if it works, or not, as soon as it cures: either it will stick, and perform as a plastic weld, or it will not adhere, at all, or very weakly... Cheers!
