I personally think an 80 or 90 size four stroke would be too heavy, unless its a superlightweight saito or something.
Think the YS 63 is the best power to weight raito for this plane, and the saito 72 slightly behind, but still really good.

For canopies,
I have used black PVC tape, but it needs replacing every 20 flights or so.
You could try cyanoing it on if you want it on to stay.......