I had an HK-clone forend from a V53 clone that I had forgotten about after I replaced it with a Surefire rail (last pic). So I figured what the heck and try it on the GSG. As you know, GSG uses cheap-ass plastic for the forend and stock. The HK-clone forend is heavier, tougher, and has a matte finish. Anyway, it snapped right on and is tight and snug. I made some tiny modifications to the edges for a perfect fit with my dremmel, but that was it. Taking it for a range test tomorrow.
With HK forend installed (GSG original is under it).