I have a RB20 flywheel that can also be used with a RB25 or 26 and can be used on a KA24 with either a RB20/25 clutch or with a 350Z clutch.
KA24 - 220mm Contact area
RB20/25/26 - 240 mm Contact area
350Z- 250 mm contact area
Bigger surface to grab onto means a stronger clutch that last longer and doesnt heat up like the smaller KA24 clutch.
$80