How to distinquish clutch size

I am looking for a clutch set up for a 1969 A108 with a 318 engine. I hear that it could be an 10" or 11" clutch . How can I be certain so once I find one I can order the correct size? And if you know where I can find a clutch , pressure plate and throw out for my van please let me know . thanks alot, Gutter

10" was the largest used on A-100's.