the light is parallel to the lens not an angle down to the subject or from the side at an angle, but straight on ...
if he used a bulb flash on his SLR, he probably removed the flash from the side mount and held it across the top of the camera above the bellows to the subject.
there were papers back then that had graphite like tones ... some of ilya1963's azo prints have that same look to them .. really beautiful stuff.
So, are you suggesting that he used an SLR and bulb flash ? Seriously ? And it had a bellows ??