You make it seem so easy :dTry to find a hoghead already set up that has a posi, (and my favorite) 3.25 or 3. 50 gears, then you swap out the whole thing, or buy the posi. unit and swap out your gears onto the new posi. unit and install, ( best left for trained mechanics).
DIY, remove drive shaft,wheels,bolts that hold backing plate and pull out axles, remove bolts that hold hoghead in, drain grease, then remove hoghead. It's heavy! Put back in-- New gasket, reverse procedure.
You're forgetting the Ford Equaloc, the precursor to the TractionLoc...Chevys have posi... Ford & Mercury have Traction lock and Detroit Lockers. Just a pet peave of mine when I hear someone say they have posi in their ford, I realize it's a loose term most people can relate, but you'll never hear me refer to a Ford locking differential as a positrac.