JUN C Series pistons are actually made by Cosworth, the W-Series are Made by Wossner and the P-Series are made by CP (Carillo) - this is from the JUN Catalogue. So you might as well go direct to the source and with going direct to CP you can choose any size you want. My experience is it is best to stay as close to stock as possible to avoid splitting bores. Running JWT in blue Z car, CP in the red Z and Cosworth in the silver one.