More pics + description of how I did it:
1 - Ditch everything but the frame tube mount clamp & ditch its clamp screw (1st pic)
2 - Notice how the barrel of the gun fits just right in the clamp. The trigger guard goes through the slot in the clamp. The gun slides in far enough that the clamp comes up to the trigger, roughly. (pics 2-5)
3 - Note that the clamp's hole lines up w/ the trigger guard. If you want to run a pin or screw through here (like the screw you tossed out in step 1), this can act as a retention system to keep your guns from falling out or being pulled out (if you little kids will break them, perhaps...?) (pic 6)
4 - (tangent) At this point, I'll point out that the gun has a switch in the barrel. ACT uses hardware from some other product that uses this switch. ACT doesn't use this switch, so they hot glue this switch in an "out" position. This bugged me, so I popped open the case, put the switch "in" (I think this required nipping off a couple of nibs on the switch, as I recall--it's been a while...), and hot glued it to the "in" position. (pic 7)
5 - The clamp comes with only 1 hole on the flat side--this is for the quick-release mechanism. I'm using this clamp "backwards". I'm using the round part to hold my gun instead of for mounting the device. So, I did some dremeling & filing to extend the slot farther & drilled 2 more holes to get 3 mount holes. 2 would be plenty, but 3 can't hurt. (pic 8 shows virgin on right, modified on left).
6 - I wanted to mount the guns on the bottom of my SlikStik panel, but my Simpsons cabinet places the control panel at a bit of a downward slope (front is lower than back). The gun's fit into the clamp wasn't snug enough to keep it from sliding out (this is a good thing, as I imagine a snug fit would start scraping the gun after repeated use). So, decided that I'd mount these vertically on the back face of my wide SlikStik Quad panel & let gravity keep the guns securely in the holsters (see pics in previous post).
There ya go! My cabinet still has a ways to go, so I haven't done any serious testing to be able to comment on long-term performance, but I think they feel & look great & should do the trick (at the right price!).
Enjoy,
-Jason