Is There an Easy Way to Know Which Size Clutch I Have?

[maverickmk]

I have now come to the part where I can actually drive my truck and on it's maiden voyage I realized why it most likely was parked. The clutch is gone. So, with that said, is there a way to tell if it's an 11" or 10" before I pull the trans? All the places I search have both listed and I would like to have all the parts on hand when I start so I can finish it in one effort. Does it even matter which one I get? It's a '69 250 cid 3 on the tree. Those are the specs I search under and get both clutch sizes.