I did this a long time back and spent hours getting it lined back up. It was hard that's all I remember about it. If you don't get it look for a camera repair shop. The 80mm on my Mamiya 645 is the sharpest of the lot, I like mine too.

If you use a screw driver on the lens be sure not to drop it onto an element. After a while a person gets tired and anything can happen. Take your time. It screws together at the same time the connection goes together as I remember. It's tricky to do.

Good luck,
Curt