Its good that you have the documentation ...
The photos didn't really do the engraving justice / I'm seeing some of the same issues as the others have commented - and while I do collect a number of guns ../and so do a lot of my buddies ....something like this would only have a limited amount of appeal / even as a novelty...unless I had some personal connection to Mr Henderson.
Even at that ...its still a Win 1200 ...with a value of maybe $300 ....even if its really unfired / and as a Henderson engraved gun, I think you'd be really lucky to get 2 or 3 times that value .....$ 600 - $ 900.../ but I think its going to be something that will not have a very wide appeal.
If you have a written appraisal that is a lot higher than that...you might check with your tax person - and see what kind of benefit you might get by donating it to a museum / or try putting it on consignment with a good dealer..see if they stir up some interest. Maybe in person ...the engraving is more appealing.../ might consider some higher quality photos ...so you can advertise it to a wider audience.