If you want a rare 450 you have to go for the 65 to 67 K0. An all original 65 would be the rare one if it had all the first year only goodies on it but I have never heard of any of them being sandcast. The 68 K1 is also going to be a good collector bike as it was the first candy color honda. The 69 is a nice bike but don't put too much money into one unless you just love it. If you have to ride your collectable bike the 68 would be much more rideable than the K0 as honda improved the gear box and oil pump that year.