Take a high-res photo for reference, combine with the scans into a single zip file and upload it to
http://www.localarcade.com Make sure that if they're in jpeg format, that you're using the lowest level of compression(retains quality the best). Some one will stitch, correct, and vectorize the artwork when they can.
300 DPI should be fine for vectorization unless there are very tiny things that may not show up at that resolution...You shouldn't need to go higher than that I think.