If you've never set up a set of gears do alot of research it can be challenging. Due to the tolerence differences in housings it is not as easy as just throwing it in. The gears need to mesh correctly, and this can take alot of trial and error in shim's. Start with the original shim's and adjust from there. I have taken old bearing's, pinion and carrier, and machined them just loose enough to be slid on and off easily so it is easier to change shim's.

Ron