If its a project, with no paperwork, then registering it for road use may prove difficult if the bike differs from its original specification and you go for Historic Vehicle class.
Up to 1970, A65 range use the same head bearings as the A10, so conventional forks will swap. Later 1971 front with upside down forks use a different bearing, so though it can be done, maybe more hassle than it's worth.
Page 82 of Roy Bacon's book "Twins and Triples"pictures what is possible, upside down forks on an A65 Frame. Page 92 shows the 1970 Rocket with conventional pre Oil in Frame type forks.
Swarfy.