On a bit of a whim I threw out a bid on what I thought was a Winchester 1885 highwall. But looking at the pictures of the lower tang, there's no serial number and the two screws seem too close together. Any idea if this is even a true Winchester?

Auction Site

You bought a highly "customised" Winchester. IMO pretty cool for the price with the Unertl scope. No serial number on the lower tang because it's been reformed (bent) into a pistol grip style which is also why the screws appear closer together. The serial number was likely lost during the shaping/polishing of it. The patent date is correct for John Brownings single shot. Once in hand maybe you'll find a gunsmiths stamp somewhere that may clue you in. Congrats, looks like it'll be fun!
BTW, Montana Vintage Arms makes parts that will fit original 1885s

Could also be that the tangs were shortened also. One I have had its tangs shortened and configured with a block of steel held between them to accept a through bolt up through the butt stock. Makes for a nifty close-coupled setup that incorporates a high combed pistol grip stock nicely suited for a benchrest target rifle, not to mention a more solid wood-metal joint that improves upon the original setup.

So it is a true Winchester, it just looks like it's serial number was removed when the tang was modified. Hopefully this doesn't hold anything up with the transfer.

I'll bet it shoots good.