Can I install a door frame with spray foam?

[demographic]

Thinking about this, if the mortar joints are big enough the old way of fitting casings/linings will work.
The old way was to chisel out a few inches of the mortar with a plugging chisel and hammer wooden wedges into the mortar joints like large wooden plugs, cut them back to a plumb line and nail or screw the casing into those wooden wedge plugs.
Gives a good mechanical fixing (worked since 1890 in my house anyway) and personally I'd stil foam them as well, it makes it all more rigid.
Thats why old carpenters sometimes still have an axe in their box, to make the slightly propellered wooden wedges that wedge and twist slightly into place.