A few things...
This is NOT factory A body width if it's 52" wheel mount to wheel mount surface. It's cut about 2.5" on each side shorter than a 57 1/8" real A body rear. No chance this fits an A body with stock spring location. Mini tub with spring relocation would be OK.
Price is relative. At $1000 it's a decent deal, not great, just a decent deal. I've bought complete Dana 60 rears from mopars with snubber provision, Strange spool and axles, 5/8 studs, 4.56 pro gear, 1350 forged yoke, 11" brakes for $800. Missed one on e-bay for $300 with 4.10's/powerlock and another shortened 4.30 moser spooled/axled unit for $450. Shortened rears don't garner big money like the factory length B and E body units.
$4000 for a Dana 60... what a crackhead! It's not a rare rear AT ALL if you know what they really were destined to be used in originally. Just because that guy is a total idiot doesn't mean the rest of the world needs to be.
Good luck with the sale.