It's going to come down to character spacing. Someday soon someone's going to use something like Fontographer to open the font, write down the character widths, numerically figure out the width of the text according to the font, and then check the copy. Then do the same thing with the IBM composer. The forgery won't be all that hard to prove, it will just take a little bit of leg work. I worked at a printing company for many years (and even made fonts) and doing something like this is tedious but not overly difficult. I only wish I still worked there--I'd have the tools and could do a thorough analysis in a day or two.
You might still need at least a better copy of the original - the differences can be obscured by the photocopy noise and distortions