right now i got 4.10 original from GM . It is 10 bolt patern 8.5 inchsWhat axle are you running in the rear?
What i have is a G-80 10 bolt 8.5 inch with eaton gov loc and cannot find nothing on how to reinstall it into my existing differential housing.I found my instructions on the internet, try Randy's Ring and Pinnion site, or just do a search.
They are easy to do, but getting a good gear pattern can take a little time. I did the front and rear in my K5, had the differential and pinnion in and out several times before I had it right. Of course the pros can whip these things out pretty fast but I am glad I did my own.