You don't see many of these sell but I'm thinking the value of an original condition one would be in the neighborhood of $1,500 to $1,800.
What I suspect happened was someone added a Poly-Choke at one point and then someone else removed that and took the 1.5" of barrel with it. This was a common modification after these left military service but I can't find any comparable sales to quote you.
So I'm gonna guess. I'd wager the barrel chop cuts a solid $700 off the value. Maybe more.
If you went the barrel replacement route, I'd remove the chopped barrel from the barrel extension and insert the new one. This isn't impossible but it's more work. The serial number is on the extension so you'd be able to keep the serials matching. That's your best bet for retaining value.
What are they asking for the barrel?