I was thinking like you and bought all the a/c brackets and pulleys from a '69 stang with the pump. it mounts aboce the PS pump. If you look on the head there are 2 tapped holes for bolts, and the pivot point for the PS pump as a 3rd.
It didn't work for me because my vac. advance doo-haab is stinking out that way, and my WH PS mount bracket raises the saggy pump up higher, putting it in the way of where the A/C pump needs to be.
Alas, I made my own bracket to fit over the alt. There is the same 3-hole bolt pattern on the psgr side, only a mirror image, so the mustang mount won't work. I cut up some old brackets I had, and paid tohave them welded up for $20. So far, I had to move the heater hose, and trim the upper radiator hose for belt clearance, as I am hookin up with the PS pump as the tensioner. No pics yet. Here are some of the mustang setups...