> How did you fasten the forms to the aluminum beam?

I attacked the problem two ways and they both worked. My first inclination was to use long sheet metal screws after drilling pilot holes through the cleats and the beam, I attached some of the forms in this manner. I then decided to use epoxy to glue the cleats on, and after roughing up the beam where the cleats attach, I applied the glue and clamped them on. The haven't come off yet and if I want to remove them or change position, I'll just use a heat gun to soften the epoxy bond.