I used the first one you linked on my FLM EXT 3906 chassis, but just had 4 out of 6 screws in place. The angled bit wasn't screwed down to the chassis, but left to hang there. Worked fine, didn't have any trouble with it. After a big jump and bottoming out, you could hear the RPM plate hitting the chassis braces. No big deal after the first time I heard it.