I'm not sure that a long tube scope will work on a Trapdoor - with that hinged breech rotating up and forward. (??) Also, most of the tube type scopes have relatively short eye relief and need to be set back closer to the eye - so the rear ocular can't be mounted forward of the breech.
Who is the Denver gunmaker? John Jamison? Petersen?
Does the stock have a screw-on pistol grip adapter or was it carved with a full PG? The reason I ask is that Freund Bros. designed some of the earliest and nicest metal and carved wooden screw-on PG adapters for straight stocks. I've seen their patented adapters on S'field trapdoors, Sharps, and Maynards.
I still occasionally see very nice un-restored Trapdoors at the really big gun shows. Prices are high by old standards, but trapdoors seem to still be the lowest price vintage American-made single shot because of the sheer number of existing examples. I don't know what a complete restoration would cost, but I'm guessing that it wouldn't "pencil out" as a wise expenditure - to many very fine un-messed-with examples out there. JMO!
Replacing the proper Buffington sight for an '84 would cost a bunch. Shooters and collectors pay a premium for that model just to have one sporting the ultimate trapdoor military sight.
This and the Hepburn you're looking for is just the sort of stuff you will likely see in abundance at Tulsa. No problem with out-of-state buying and returning home with antique arms - and Cash is King. I have a feeling that there are going to be some real bargains available on some of the old firearms you and I are so interested in - for those with cash-in-hand. Some of the folks with tables get really weary of the yahoos wanting to trade their armload of Mossberg pumps for the Sharps rifle laying there.
Grab Mrs. giz and the Lord Slashcats and make a vacation of it. Even if you've already been to visit, there's always something new at the Gilcrease: