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.
xtm