They are from an R34GT-T.
This caliper is identical to the R33 GTS caliper. It's just that the "legs" are a little longer to accomodate a larger rotor.
R33 GTS --> 296mm rotor diameter
R34 GT-T --> 310mm rotor diameter
I don't own a skyline myself, but from what I understand, this is a nice upgrade for people with all sorts of cars - especially nissan owners.