Congratulations on a great looking rifle and welcome to the club - albeit a very addictive club!!
Might I suggest that you try the Williams before removing it for the screw-up Marble. I have had good luck with both. But one time, I had two rifles that looked the same, were the same caliber, but one had the peep (Redfield) and the other the screw-up tang (Marble). I found that on that particular set of rifles the peep worked better for me. Also, I had to replace the front sight with a taller post when using the screw-up on a couple of other 8/81's.
AS TO FINISHES, I copied this to use in refinishing some stocks on older rifles - the idea came from an 81Police's post some where on this forum (not an exact quote and I have not tried it yet):
To closely duplicate a factory (pre 1950) varnish finish: recommend a satin or semi-gloss (urethane /varnish?) cut with 50% linseed oil* then hand-rubbed - can get a very close match.
This regarding
Lin-Speed recommended by an Old(er) Timer "as the ONLY FINISH to use on stocks" at least it was back in the 40's and 50's (seems that a bunch of folks still like it, as it's still around!):
... from the Lin-Speed web page: "...(Lin-Speed is) linseed oil refined to the point that the oil acquires the admirable qualities of good body and rapid dry. Ordinary linseed oil never really dries. The "GB" Lin-Speed refinement process removes the non-drying linseed parts (called Foots)."
Enjoy your new treasure, a real part of firearms history for sure!

Though defensive violence will always be “a sad necessity” in the eyes of men of principle, it would be still more unfortunate if wrongdoers should dominate just men. - St. Augustine