For the first few years of the telescopic forks (1948-50 approx), the fork legs are closer together than in the 1950 onwards models, so it is not possible to mix and match the top and bottom yokes.
I think there were four different types of top yokes (not including competition models), a steel narrow yoke (1948-50), a steel wider yoke for remote speedo fixing (1950-52), an alloy yoke with central speedo hole (1952-55), and a steel wider yoke for the nacelle models (1956-59). The second and fourth types differ by the later having a bend out and down to the fork legs.
The first bottom yokes have to match the narrow top yokes, the later wider ones are generally interchangeable, although for the last few years a steering lock was incorporated in the bottom lock, with a matching piece on the frame to accommodate the locking pin.
If I have missed out any different types of yokes, please correct the above.
The first two types are not easy to find/buy these days, the later two more common.