You can scan the photo and use photoshop to clean up the imperfections (scratches, discoloration, contrast) then print from the file yourself or bring it to a photolab. As a precaution write a letter stating that you have checked into any copyright ownership of the image and none was found. Dont give this to the lab unless they ask. You should have no trouble.

I have never had a photo lab ask me anything except "when do you want it?": i have copied many old photos of ancestors.

I wouldn't expect a problem with the copyright if you are just reprinting the pic for family members. Could be problem if you plan to post it in public view, like the Internet.
If you are really worried, ask the phototog. If there isn't one to contact and it has been 70 years, then what can you really do to protect yourself, not much.
After a certain time(Canadian Law and I can't see the US being much different) a picture becomes part of public domain and anyone can use it. Fifty years must pass after the death of the person who took the picture for it to be a non-issue. See here- http://www.cipo.ic.gc.ca/eic/site/cipointernet-int ernetopic.nsf/eng/wr00506.html

Almost everything created privately and originally after April 1, 1989 is copyrighted and protected whether it has a notice or not according to US law.

Unless the photo is part of an image library owned by a photographer or company having purchased the rights to the shot, its not likely to be a problem for you.

Sureyou can.
any photo lab with new equipments can make it for you