If these are art-quality, valuable photographs, keep in mind that it would be best to keep them in pristine condition, and any change, including permanent mounting, may reduce their value. On the other hand, since glazing will not be used and their surfaces will be exposed to open air, they probably will deteriorate quickly or be damaged anyway.
As mounting adhesives go, aerosol sprays make the weakest, least-durable bonds, and PMA is not much better. I would avoid it.
Heat-activated, low temperature adhesives are easy to use, make very good bonds, and you have choices. MountCor is thermosetting, which means the adhesive can be activated only once, so if removal becomes necessary, use a solvent. Kool Tack is thermoplastic, which means that the adhesive can be reactivated by reheating, so if removal becomes necessary, reheat it.
Both of these products operate at temperatures safe for almost any inkset or art medium. Kool Tack offers several substrates including aluminum composite material (they call it Competition Plate), and maybe MountCor does, as well. If you want to avoid buying a full carton of the low-temperature, pre-adhesive dry mounting board you choose, perhaps you could buy only what you need from a friendly framer in your area.