Yes a 12 inch clutch will work on the stock flywheel. I first converted to a 12 inch clutch on my 68 KM-2500 30 years ago. Basically it was a Webber replacement clutch for newer trucks built in the 80's but also an upgrade for earlier model, the pressure plate bolted right up to the stock V6 flywheel. What needs to be done when resurfacing the flywheel is to make sure the entire circumference of the face is resurfaced for the larger clutch disc.
