I refinished my Model 39A when I was in high school in the '60s. It did lighten up the wood a little. It was probably stained by the factory. The 1969 vintage Mountie I bought last year has pretty good wood and I haven't done anything to it.
The sights are easily fixed. I like the Redfield receiver sight I put on my 39A all these years ago, but today, the receiver sight I like best is the Williams Foolproof. I put one on the Mountie along with a XS Systems white outline square post front sight. The combination provides me a very nice sight picture. I have played with scopes on the Marlins over the years, but I think they are more appropriate with iron sights.