Just keep the stock exhaust. You can get into the low 40s with no expansion chamber. I built one the other day and it is so good, I almost refuse to put big pipes on people’s “stock” maxi’s. Unless you’re tryin to burn up clutches and beat your friends to the top of that hill it really is the best. I can’t stand loud, dragging pipes that get in the way anymore.
For the kit I pretty much always go for the airsal 44; it is very nice and torquey, and assuming you have a 1.5 or 2hp low torque maxi you can use the stock head, and it doesn’t feel anemic with the original carb. For preparing the cylinder there is very little to do with this one, I usually just plug the decompression hole with an m6 set screw and run a bit of sandpaper around the shape edges of the piston, but it does have plenty of potential if you want to get crazy porting. My only complaint is cylinder plating is very thin so be careful if you’re doing any filing or a pit a rotary tool to the ports that you don’t chip it.