Does anyone know which size caliper wood have to be used in order to change over to the Willwood brakes? I have seen a pic of a sentra or 200sx which had these calipers.
The bottom of the this page from this link shows all of their available caliper sizes and types, one of these has to fit.
http://www.precisionbrakescompany.com/wilwood_billet_superlite.html :D

I meant would not wood.

To my knowledge, Wilwood are a kit. It's the whole deal. Rotors, calipers, pads, and I think, steel braided lines, not sure about that.