Yes, Doc, It's a 1964 Greeves Challenger MX1, of Dave Bickers, Malcolm Smith & Dick Mann fame. I think even Joel Robert (now that's a familiar name) rode a Greeves for a while prior to his time with CZ, but he rode the MDS, the previous model to this. I'd love to have this back in my shed!
Great forks for their time, Wombat, very stable under brakes - something to do with the front end geometry remaining constant over the full travel. Until Ceriani forks became available with more travel(6in) and lighter weight, they were great.