Q. Dear Donia,
A. Dear Todd,
To the best of my knowledge (I am not up on all the solutions used in that time-frame) most of the retouching fluids were solvent based so as not to interact with the image layer of the photograph. Which solvent would work to remove the paint requires training and a very exacting hand, otherwise, you could do more damage to the image than the paint is distracting. The best thing to do would be to consult with a photo conservator and, being in NYC, you should not have a problem finding one. You can get a list of names from the Find a Conservator page at the American Institute for Conservation. A conservator who specializes in photographs would be able to tell you more as they have more direct experience with the medium.