As far as I can tell it'll fit, but what is your dad hoping to gain by going to carbon? Cause he's not going to save much weight; the 1-1/8" one is 722g. It might be slightly comfier, though.

And what about the unused canti posts, won't they look silly? Oh wait, the bike already looks like that...

I guess there are better forks out there, but not likely at that price.