Hi, (First of all. It's supposed to be 3G and 4G, not U. Sorry for that mistake!) I was wondering if it's possible to 'shape' a 3G grip into a 4G?
Sandpaper will be all you need. What I do is mark out some line, starting at the main bevels, sand it down to that line, and then do the same for the opposite side, then the side bevels and finally the smallest 4 bevels.