GURPS is indeed an exellent fit for Hârn, especially on the mundane side of things.
One instrument that GURPS 4e has for powers and spells that 3e didn't is the whole GURPS: Powers
side of the game - the crafting of spells and (super)powers et al. using mostly Advantages and modifying the hell out of those.
There are also a lot of options for modification of the GURPS: Magic
system available in GURPS: Thaumatology
that will help break up the spells and the way they are gained/learned to make it a bit more "Hârnlike".
But the basic approach of college assignment to convocations for Shek-P'var still works quite ok.Some musings of mine
from a couple of years ago or so. Only got so far that time (may be it's time to take it up again?). I think the most comprehensive compilation out there right now is the one by Techtutilay
of the SJgames forums - though I find that his approaches go too far in making EVERYTHING like HarnMaster - but YMMV.
Harniac. That simple
I'm intolerant of intolerance. Intolerant people find that very hard to tolerate.