The gap in the channel would be huge not to mention most likely a difference in the receiver as well, but that's beyond my knowledge. A 2 contour barrel would swim in a 4 contour, IMO it would look terrible
If you have an accumark by chance which is a 3 - pull it and put on a deluxe and you'll get a picture of just how much bigger a 4 would be.
What are you looking for in a stock? Someone here might have one, including myself;