It is a year ago today that you posted your query and I don't see that anyone answered you. My problem is similar. I have a Mac 1988 PAF 2.1 that makes a GEDCOM 2.1, however I need a GEDCOM 5.5 or better to move all my extensive data to a new Mac Family Tree Maker.
How can I convert my Mac GEDCOM 2.1 to Mac GEDCOM 5.5? Help!
Did you make any discoveries in how to solve your/my problem?
Have a happy and blessed 2011.