When the 1969 CB750's snapped the master links on their weak drivechains, the crankcases suffered catastrpophic damage from the balled-up pile of chain links. Dealers replaced the crankcases under warranty with a diecast set that had no numbers, and used the rest of the original sandcast engine guts for the rebuild. Corresponding oil pan and clutch cover were included, and a new endless chain was also peened on. At same time, the round oil filter, thin throttle cables (along w/ a notch cut out of frame by dealer for extra clearance), and a short chainguard were all replaced by dealer as per Honda. I've owned a motor w/o numbers in a sandcast frame, crankcase set was diecast.