i know that FSA makes the cranks to fit either octalink, or the ISO spindles. i'm pretty sure that they also make them with the square taper (that campy uses). if you're talking about the gossamer cross cranks, i have them on my road bike at the moment, and they're pretty nice. the inner ring is 38T, not much difference from a 39, and they use the same BCD, so you should be able to put a 38T ring on your campy cranks. if you want smaller, i'd say go with the triple if FSA makes it, which i know they do for road, and i can't really see that there'd be any difference between the 'cross and the road versions, other than chainring size.