Digital BW, The Print

There's obviously some physically damaged film emulsion in Brandt's
process.

It varies quite a bit, and is sometimes much more than an edge
effect..it pervades as much as half the image in some instances. I
don't like what I see in some of it, like other examples a lot.

Your initial guess that he was using glass plates may be correct in
this way: He may be mounting interpositives (from his 6X7 negs...he's
a FILM guy, not a digital guy) in glass mounts, then damaging them
with heat/moisture/chems, then Photoshopping. 

He could reasonably make dozens of interpositives of each of his rare
B&W negative images, damaging them all and looking for the one that he
likes best for each original negative.  

Per Steve K, Polaroid PN could be part of one solution, and floating
emulsions off could be one approach, but having participated in that
with Ektachrome sheet film, I think that's one hell of a frustrating
way to go...and expensive. 

Since you're a digital guy and don't have a real medium format camera
(645 doesn't qualify IMO), I'd suggest you take your large fine print
to an old fashioned fanatic hobbiest that can do proper copy work and
ask him for a bunch of 6X7 or lantern slide formatted shots, of
whatever film type is convenient. Then mount them in lantern slide
glass, which can be found if you look hard enough, then go to work
destroying the edges :-)

Photoshop won't care if you're working positive or negative.