The intention of that particular self tacker is for it to be able to pivot and align itself with the sheet loads. The original Nacra self tacker on the I20 was a molded fiberglass fitting that riveted to the main beam, but because it wasn't able to align itself to the loads it often cracked because of misalignment. In order for that self tacker you have to pivot, all of the pins that hold it to the beam must be in a straight line - otherwise, it will not move once you pin it in place.

I might consider first mounting the self tacker to a straight piece of aluminum angle or tubing and then mount that tubing to the beam...but it would still be tricky. You could cut and bend the ends of the angle to give a mating surface...attach on the bottom on both ends and on the leading face in the middle.