Yes. The crankcase ventilation is different, so you need a 69 inlet cam if you want to go that route. It's easy enough to convert the 69 cases to breath through the primary though, like on the OIF models. If you plan to fit the 69 top end, you're less fortunate, as it won't easily fit. Plenty of help to be had on here if you need it, just state what you have, and want to do.
The cases will fit in the frame, but some of the internal components may not be so easily swapped. As well as the rocker boxes Roger mentioned, Triumph started going to metric bearings in mid 71, IIRC, so the crank and those bits need to stay with the right year cases.
Thanks for your replies. I have a fit and healthy (roughly) T65. Any value, over and above the standard TR6r, is in correct stamped numbers. I am looking for insurance in the form of unstamped cases as replacements should the need arise.