Few pics attached.
Trying to put a value on this gun.
Unable to find any that have sold in the last few years.
Notes on the gun;
Few pics attached.
Here are notes on the gun;
It has a brass center bead with Ivory front on smooth concave rib that is marked with large engraved letters "John Rigby & Co. Dublin & London".
Side plates are marked "Jno. Rigby & Co.".
John Rigby (Dublin & London), 20 ga dbl, top lever, hammers, 28” damascus
JOHN RIGBY 1885 20 gauge double hammer top lever shotgun
One of the first built in 1885
14 3/4 L.O.P.
Butt stock sanded and re-varnished or a replacement
Forearm wood and metal matching numbers, solid, all original
Marking
NOT FOR BALL
20B means “bore”, 19M means muzzle in the meaning that the gun is choked and not suitable for ball.
136 Years old
Bores show very few minor rough spots of light pitting.
Damascus pattern worn - silver finish.
Traces of case colors still showing.
Engraving excellent, hammers original with no issues, functions just fine, short chambers, tight on face.

A very nice gun but that poor quality restock kills the potential value. My feeling is you have a 3500-4500$ gun. With original wood, good bores and walls that would be a 10K plus gun. You sure do not see many 20 bore Rigby top lever hammer guns. If the tubes check out, that one would be worth a proper re-stock. Best of luck with your sale.

Obvious restock. No way that leaves Rigby with the rough finish behind the hammers and around the top tang.

You gave a lot of important information but not two of the key ones for me. Chambers still 2 1/2"? What are the minimum barrel wall thickness? A lot of the small bores I see have very thin MWT. It they are too thin that gun will be very difficult to sell at any price with that replacement stock. Wish you good fortunes.