Big Marlin Lever fan
I DESPISE the guide gun or railed look on them, and although some like it, I believe that look cuts your market considerably.
Parkerizing a lever (again IMHO) makes it look as though the gun was REALLY beat to hell and is getting covered up.
IMHO they are best left pretty well stock, and the many, many GB auctions I've followed on 357 Marlins bear that out.
Value of a shooter can rise drastically with a dent-steam and tru-oil refinish of the wood and a reblue or touch up with cold blue if wear is minimal.
I haven't refurbed any checkered stocks, but sounds like you might have better skill in that regard.
I say steam out/spruce up the wood, gloss blue the metal, install the big loop (which I think will make it very desirable) and pop on a Skinner sight if you feel like it - I would not go with Big Dot or Fiber Optic.
If you want to personalize a gun and keep it forever, that's one thing, but the closer you get to frankengun status, the fewer will have interest in your rifle.
Unless you have an octagon Cowboy, you're already running an 18.5" barrel...a chop to 16.5" might be interesting, but I've never done it.