Ideas? why sure!
Run metal electrical conduit out of each of those four vent holes below the sight rail. (the flexible kind, that's all ridgey)
Attach a battery of old-timey-looking capacitors or even a little pressure tank to the opposite side of the gun and connect the conduit to it.
Attach brass flourishes to the barrel, & stock.
Put a "Doc Brown" looking scope on the top sight rail.
Barring that, put a very long old fashioned scope on it. (The kind that is the length of the whole gun.)
Bend up a fake lever-action-style hand and trigger guard for it.
Bayonet

That all sounds awesome, doable, and best of all cheap!
Now the only small part is that I only know what half of those look like, and even less on where to get them haha!
So, metal electrical conduit... where can I find it, and what do you mean by run it out of the holes? They're just shallow circular cutouts of the plastic, unless I bore holes into the actual gun plastic if that's what you meant.
Tgis one is fun...old-timey-looking battery with capacitors and a little pressure tank. Not a clue as to what those look like or where to get one, if you have a link, I'll bake you a pie.
brass flourishes... no idea what those are lol.
Doc Brown scope... any idea where I might find a good one cheap? I suppose I can check the Flea market I have up here on Sunday, but in the meanwhile, an idea of just what it looks like would help.
The bend up fake lever-action style hand and trigger guard, actually don't knwo what you meant by that. Could you elaborate a little more?
But seriously, thank you for those ideas... they sound really quite good and something I can probably do.