for ur info usually if u purchase one whole set, it will come together wif the callipers + disc brake. and u dun need to modify it cus if im not mistaken Waja is using 114.3 PCD which is the same as the VR4s one. i sort of surveyed lastime, got this chop shop selling loose parts like callipers or disc brake only but it is quite expensive as u know le, loose parts usually are not worth it to get unless in a set.
good luck