I am not the one who did the HARP/Harn PDF (though I did do a little consulting with the fellow who did do it).
If you go to this link, you can download a VERY VERY early RMSS/Harn thing that I worked up many many years ago (before I ever worked for Mjolnir/ICE)
http://www.wizlair.net/downloads?did=19The trickiest part, I think is going to be reworking the spells to form the 6 convocations you find in Harn, and creating the mechanism for a character to become a Grey Mage. But that is okay, because the way that the Mage (Classic) is setup, it will be easy to work in the special costs for each Convocation -- such as follows:
Primary = 1/2/4/6/8/10/12/15
Secondary = 2/3/5/7/9/11/13/15
Tertiary = 3/5/7/9/11/13/15/15
Opposing = 3/5/7/9/11/13/15/15
(note: the cost breaks every 5 ranks)
And of course, the rules from Libram Novus #1 would apply as well (since journeyman mages are supposed to return after a year and a day and have a new spell and/or item for the guild.