Dave: My parts books only go back to 65 for the unit engines. That year for the A65 lists two fork tubes, 68 5030 for the cranked top triple and 89 5061 for the others. Both of these tubes would not use the rod damper that came out the next year. 89 5061 is also the Gold Star scrambles tube.
Those tubes would all have two small holes near the bottom like these as far as I know.
In 1966 the A65 does not list the cranked top triple and lists only had one tube, 68 5144 and shows the rod damper for the first time. The bottom holes for these tube are different from previous tubes. There are now four larger holes spaced evenly around the tube and all the same distance up the tube. They look like this. The bottom screw in fitting may or may not be the same as the one shown here.
To switch to the BSA rod damper you would only need top cap with the threaded inside hole (or the through hole with a nut on each side) the damper bits and the slider with the hole at the bottom to anchor the damper tube. The top bushing is not secured with a circlip like the earlier forks so you most likely would need a different seal holder set up.
As for the tubes one could take the shorter early A65 tube and use it in a rod damper setup but I would think that the holes at the bottom would need to be changed to the four larger holes vice the two small ones for it to work as BSA intended.
However there may well be a shorter tube from one of the non A65 models. The B44 Victor Enduro used a rod damper fork with tube 41 5115 (vice 68 5144) using the same damper tube as the A65 but with a different damper rod 41 5128 vice the A65 damper rod 68 5143. I do not know how long the 41 5115 tube is.