I've recently been thinking back to my OD&D project, which I've basically scrapped for a replacement project. Instead of trying to convert OD&D to FUDGE, I've decided the idea of converting OD&D to anything is just silly; the game is too much a mess. Instead I'm poking and prodding it for deconstruction, to gain insights and harvest ideas to inspire a new game in that broader pseudo-medieval fantasy genre.
Today I've been thinking about ability scores and the OD&D presentation of them as "categories of ability." I like the idea of having a small list of ability categories that can be used in place of long skill lists; abilities as action types instead of attributes. I don't know that I'd necessarily want to stick with the traditional six abilities, though, especially since their names fit the concept of attributes better than abilities.
What sorts of abilities should there be, though? A big part of that would involve the game's trappings; which things make sense for the setting and style? One way to mimic D&D's trappings could be to break the core classes into archetypal categories: fighter as Body, magic-user as Mind, cleric as Spirit. Then perhaps the equivalent of strength is Body*2; Constitution, Body+Spirit; Wisdom, Spirit*2; Charisma, Mind+Spirit; Intelligence, Mind*2; and Dexterity, Body+Mind.
That seems more like just creating a shorter list of attributes to mimic the same six, though. Supporting the abilities concept might require looking at skill categories; things like battle, consort, craft, explore, research, etc.