I just bought this one, from a local dealer, either a 51 or 52 seems to be the general opinion from the group here (S/N K 128XXX range). No box or papers, but all numbers match. It was tagged at $700, I got it for $650.
How much is the box worth? I don't know. I'd like to have the box, but I got no idea how much more it would add to the price.
Well, maybe I got some idea. Not long before this one, I bought a 38 M&P, 6" barrel, also from that 51...maybe 52 time period, all matching numbers, with the box that was originally tagged at $750, I paid $675 for it. Same dealer.
The box.
I don't know if that will help on not, but those are real world, recent experience. I got no idea if I got a good price, or got took. In the end it really comes down to how bad you want it, vs how bad does he want to sell it?