Rear End Swap Question

[Shak]

I'm sure this question has been answered before, but I just couldn't find it anywhere. I am in the process of a 67 C10, lwb build. I am going to swap out the front drums to disks, and I'm trying to decide on keeping the 6 lug bolt pattern, or going to 5 bolt, which increases my wheel choices. If I go to 5 bolt in front, I'll have to do something with the rear as well. If I decide to swap the entire rear end (which will give me some gearing and posi possibilities), which vehicles have compatible units, ie: same size, etc. I will be running a mild crate motor with a 700r4 tranny, and a 4-6 drop, if that factors into the equation at all. I am new to this, so any help is appreciated.