First of all - Welcome to the forum!
I would expect that the stocks in question look a little like this:
These are Fitz stocks on an early 4-screw Model 48. I don't think they add to the value, but they probably do not detract from it either. They are comfortable in my hand and so they will probably stay on the 48. Interesting to note - most of the later Fitz stocks that I have seen are the same shape but they were made from some sort of plastic.
Let's see a couple of photos... I love the Outdoorsman's and I have some aftermarket target stocks on one of my post war ones. I like them too, but I think they are made by Sile or Stile (something like that - I just cannot remember). They are on the top gun in this photo (the bottom gun has the factory stocks):
