On my 4X I use 64p gears but I don't see why you couldn't use 48p gears if thats what you have. You would just need to find a 48p gear with the right mounting holes. As for changing the spur and motor Serpent has made it very easy. The layshaft comes out with two screws and the motor as well with the standard 2 screws holding it to the mount. There should be no need to remove any other parts to change both out.