If you are talking about changing out the gears in the rearend of a 1 Ton, the whole assembly comes out the front in one piece. There is a tech Tip on it. The 4.10 setup can be hard to find but it really makes a difference.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!