An excellent question! There is a good FWB 300 discussion group on Facebook, where Scott Pilkington recently put up the image below. The gun on the left is a 300S action, placed into a gorgeous custom stock obviously designed to match the center fire beauty on the right (both of 'em lefties, too). So you aren't the first to ask, LOL - I've wondered why FWB didn't do something like this themselves.
As you can see from the posts above, the earlier models 150 and 300 had a stock fore end that was shallower than on the 300S. I have a 300, and while I love the lines of it, to be honest I would not really call it a "sporter" stock. The fore end is longer than the 300S, and actually slightly wider. When you pick one up, you definitely don't forget you have a heavy match rifle in your hands.
A major factor in how the 300S handles is the barrel weight. Contrary to appearances, this is not a separate piece on the end of the barrel, but a full-length sleeve that is fatter at the end - the actual barrel is only 15 mm in diameter. The sleeve was a factory option, so there are guns out there without one, and not having that weight out there so far in front of your hands makes a HUGE difference. You may find this is the key to your question; you aren't going to shave 3 pounds off the gun by changing the wood.
My current favorite FWB shooter is this one - a Junior ("Mini") action in a 300SL stock. The Junior has a shorter barrel with no sleeve, and the "L" stock is similar to the basic "Match" model of the day, but with a longer fore end and extensive stippling. It's still no R7 in the handling department, but a lot more "sporter-y" than my other 300's for sure.