I would go look on team chevelle to get some ideas. But seems like most posi 12 bolts seem to get $1000+ depending on condition and how complete it is.
Posi probably need to be re-built or replaced, are you really going to use those gears, then new axels, axel bearings, pinion and carrier bearingc, maybe backing plates, cleaned and painted, what about worn control arm bushing bolt holes. Then you need someone who can set up the gears, no super shims on a 67, one shim per side.