The two trikes I've seen had a chain final drive. If it's engine power your concerned with could you change to a smaller front sprocket? Lowering the final drive ratio.
Actually, I don't give a chit. I just started that post to see what kind of information other people had The trike does me just fine. I'm not after another 2 mph, 1.5 mpg, 0 - 60 in 44 vs 45 seconds, etc.
I got it to ride and have fun.
Actually, I was quite pleased that 300cc thing moves 1000 lbs as good as it does, so, why mess with what works.