Is he wanting 800 for a complete rear end or just the chunk? Kinda high for a complete rear unless everything is new in it and then it's not a bad price.
Chryler products used a 4 1/2" bolt circle as far back as I can remember. The 'A' bodies used a 4" bc until they started installing disc brakes as standard equipment in 73 and then they went to the 4 1/2" bc. Many Fords also used the 4 1/2 bc too but had a smaller center hole. The Dodge pickups also used it until around 85 and then went to the 5" bc. Dakotas also used the 4 1/2" on 5 until around 91 when they went to a 6 hole wheel but still on a 4 1/2" bc. And yup, the 8 3/4 rear end is a good unit...