I finally got around to the Marker Beacon antenna today, as part of preparing the fuselage for doing the side skins. I located it on the right side inboard of the innermost system bracket by about 1.5" where the bottom skins overlapped. Even though I measured carefully, I wasn't very happy with how the screw holes ended up - I do wish Comant proviced drilling templates. However, it was clear that even the doubled skin thicknesses would not be enough to keep the antenna bolts from bottoming before they were tight, so I cut a doubler from .060" alclad and used the existing holes in the skins to mark the screw locations in it and got a better result on the inside. Once the doubler was installed, the antenna was secure with no movement possible from the elongated holes in the skin, which were also hidden by the antenna. By the way, the elongations weren't that much, just enough that I would have worried about the antenna 'working' in them; the doubler fixed that nicely.