About larger rear sprockets...in the 70's, I had a 175 Yamaha Enduro. I wanted a larger rear for off road but I rode it to work and needed the stock sprocket. Someone told me about an easy quick change conversion.
At that time, you could get a larger sprocket with a center hole that was made to fit exactly over the stock one. It had 4 notches to put 4 bolts between the teeth of the stock sprocket to hold it in place. I don't remember tooth counts, but it added about 2" to the outside diameter. Of course you had to drop the rear wheel to put it on. This conversion avoided that. You could put it on by just breaking the chain.
I drew a line straight across it, crossing the center as close as possible. I drilled holes on both sides of the line to match the pins in a chain link, 2 links on each side. Then I cut the sprocket in half. To install it, put the 2 halves over the stock sprocket and insert 4 chain links through the holes. Then put in the 4 bolts through the teeth as it was designed to have. Add the necessary extra chain and tighten it. Once it's set up, installing it took about 15 min and it worked perfectly. It wasn't balanced enough for high speed but for off road it was great.
