A few hundred, if you want to sell it sooner then later, a couple hundred. About the same as a well used 1985 4hp outboard, maybe even a little less because it shouldnt be run as is, and a regularly used 4hp could be shown as running prior to sale.
Unless you find a guy whose grandad or father had 1, and they WANT another JUST like it. Then maybe 1.5-2times more. But you'll be waiting a bit for that buyer....