Nice build, congrats. Thinking about your drive roller, see if you can find a piece of heater hose with an inside diameter around the same as the outside diameter of the socket that you can put over it. If it's a tiny bit smaller, even better. Best case would be a hose that has to be soaked in hot water for a few mins to soften while keeping the roller in the freezer. Slide the now warm, pliable hose over the socket. When the socket warms and the hose cools, they should be nearly inseperable.
If you can't do that trick, maybe try "Magic Wrap" tape
. It's useless where there's fuel (turns to mush and disolves), but it works pretty well in other applications. It could also be used as a shim layer between the roller and a piece of hose as above.
Just some thoughts there, I haven't worked with friction drive (yet) myself, but it could work.