lurcher - I'm not certain about this but I think the synthetic stocks are a bit heavier than the wood stocks are. I would liek to think that if you are trying to keep the weight down, a synthetic might not be the way to go.
Also, you mentioned cutting your barrel back to 20". Is that 96 carrying a 29" bbl now? The M38s wear a 23" bbl and mine is pretty sweet and I think that is as short as I would want to go. You spoke to fluting the bolt and drilling a hole in the end of the bolt knob - all that would certainly customize your rifle and its looks but would it reduce the weight by any significant amount? I would hate to see you go through all of that work with a beautiful Carl Gustav, and then not be happy with it or have an unbalanced rifle that didn't feel good in your hands or when you brought it to your shoulder.
But, alla this is just my two cents worth. Mikey.