The early S110 rear discs and calipers I got were small and very light and fit under 13's. The discs were same as R31 skyline and the calipers had postage stamp pads in small light calipers. This came from an import S110 SX? with Z20E I got from an import in Christchurch a few years back.
I think going up to 14's would be a step back as good circuit rubber is not as easy to get and you would be increasing unsprung mass. My two bobs worth.