These are color Ilfochromes, and I'm not using heat, or a press of any kind. I've tried all manners of "tacky board", the 3M roll adhesive that is repositionable onto all sorts of smooth substrates, and Koda cold mounts. All mounts were using very lite pressure, and super smooth cover sheets. Every technique results in some surface orange peel.
I guess poly based papers are meant to be hinge mounted, but that doesn't work for me, as I sell them at outdoor shows, and have seen wrinkling from humidity.