I really prefer something longer than "normal" per format. You'll get better field illumination and probably better
definition near the corners, esp at relatively wide apertures. Something like 105 would be better than 75 in this respect. But forty inches is huge for medium format. A mural lens like Rodagon G might be appropriate, though it
would be an inferior performer at ordinary scales of magnification (it's a specialty enlarging lens, not a general
purpose one). Just depends how fussy you are and what you can spend. Think I'd rather have a 105 Apo Rodagon N instead of a G, just for the greater versatility. But even ordinary El Nikkors or Rodagons will do a pretty decent job, if you can't locate one of the Apo ones.