I would swing through gunbroker.com & gunsamerica.com & see what you can find similar. Gunlist magazine online classifieds may also show something. Of course listed price & selling price can have a little margin.
Roughly $1500-1750 +/- a few bucks if you find the right buyer. How are the barrels choked? That makes a difference.
I have an old Lightning Superposed 20 choked skeet/skeet that I have USED. I got it in 1973 and many, many quail have hit the skillet as a result of that gun.
I have the same gun 28" rechoked to IC and IMP MOD and it has been the demise of a pile of ducks, pheasants and late season grouse, it would take a pretty piece of change to get it away from me.
Chokes are IC and MOD. Gun serial number is from '73 I beleive.
I have looked at Cabelas Gun library and GunBroker... with the values at sale in the $2000 to $4000 area. With those values I was curious how to be most accurate. Not sure that demand is great for this type of firearm.
Those are 'asking' prices /ubbthreads/images/graemlins/smile.gif. There's a gun shop in Houston that deals in collectibles. I forget their name. They can give you an idea of the current market and they might take consignments. They sell a LOT of very nice guns.
I sold a Belgian Browning Superlight two years ago. Fixed chokes, straight stock, Grade I. 20 gauge. 26 " barrels. 99% with the box and papers. Had it for sale on Guns America for one day. Sold to a gent in Utah for $4800.00.