Not sure about the forend, but I think the old "wedge" shaped forends fit the tapered barrels better that the bull barrel models.
With regard to the Duo Ring mount, it has a much smaller footprint. I just measured a used one that I picked up. It is 1/2" X 2 5/8". The Duo Ring is starting to become my favorite mount. I like the looks, and it is a good solid mount.