[SCOTI]

71's came w/5-lug 12-bolt housings. If it's indeed a 10-bolt, it was swapped for a later model rear-end @ some point.

As for if it's a "good buy" or not, how many of the remaining parts can you use toward your project? If you use most of it, then it's not $$ wasted on stuff that goes unused.

The front of the 63-87 1/2 ton trucks can be static dropped around 6" max using factory stuff w/o mods. At that point you have to be concerned w/the lower a-arm bushings & x-member contacting the ground. A larger truck will typically be slightly higher off the ground so it can go more (6-8") before there are clearance issues on the bottom. The trick is the issue typically becomes clearance within the wheel wells depending on overall tire heights used.