need help with rearend question about a c20 van

[sev85]

hey guys i need some help i have the chance to buy a posi trac rearend out of a 1993 c20 van 12 bolt posi gears are unknown i was told it is a 6x5.5 lug patter would this rearend fit under my truck and would i be able to swap in my ring and pinion gear so i can use my gear ratio?

and would it be worth 100 bucks for the whole housing or should i just buy the internals for my housing?

i forgot to mention my truck is a 1982 gmc high sierra 400 sbc th350 203 transfer case with part time kit front end is a gm corporate 0 bolt 3.42 ratio rear end is a gm corporate 12 bolt limited slip 3.42 ratio