I don't think there's much I can do about the forend when machining aluminum is involved. I'm trying to keep the kits reasonably priced. The rail even on a 6.5 should be long enough for a forgrip, but you're pushing the 660mm oal too close if you deviate from a factory length stock. Forget about a Tac IV-S. I think it's too short. I also don't know if we will make them any shorter than 8.8". We'll see how much interest is generated.