well, for all the masochists, this is a great image
it's VERY far gone. i did QUITE a bit of speculation on the face. i first split the image into rgb, then hsl, then cmyk. i took the best of those channels and put them back together as an rgb. it still didnt give me much better than the original. there was only one even partially decent channel per each of those modes and they were all pretty much the same.
so, i simply guessed. but, i stopped this well short of doing too much. i just wanted to give a general idea of where this might go. besides, this is a heartache picture. no matter how much you work on it, you're going to end up in a heartache.
one thing i would ask here, did the gentleman wear glasses? there was a tiny indication that he might have.
also, some of that junk on the image looks like fingerprints. you might be able to get the image cleaned physically and get a better scan after.
also, if this is one of those old red proofs, be VERY careful in handling it. i have some at home and they'll degrade pretty badly, pretty quickly, to where the red film will actually start peeling and flaking off the media. yours doesnt look like it's hit this stage yet, thankfully. i have one at home that i have to handle with tweezers.
also, if this is for a client, you want to be sure to tell them ahead of time, before doing any work, that this is going to NOT be very satisfactory, no matter what you do. put that disclaimer in early and make sure they understand this. i would also consult with them frequently and show them your progress and time sheet and ask if they want you to keep going or not. you could put in a LOT of time and still not be very happy with your results.
anyways, here's just a very rough idea of what might be... 1000 folks could work on this and come up 1000 different ways and i wouldnt argue that any of them were wrong.