It turns out there is a bit of thread on the bottom of the regulator, and it seems to be the same size as a AN924-5D nut. To be honest, it felt just a bit too big, but it threads on nicely, and I could tighten it just fine.

I made the bracket out of 1 1/2"x2" angle. You can see the blue nut on there.

Here I've got the hose clamped on there, which actually acts as a bit of extra security. It's jammed up there quite tightly. I think this will hold fine. The two oetiker clamps that are close together hold the small pressure relief valve, which will allow the pumps to self-prime in case they suck air or vapor. This is a bit of vapor lock security.