Either get an earlier 500/550/750 hub with the flats; cut two flats on yours; drill ant tap the hub and hold the plate on with countersunk cap screws
I pretty much agree with the above suggestions.
BEST solution:
The least expensive (and best) route would be to drill & countersink the driver and drill & tap the hub to retain the driver. Mount the driver to the hub, drill both, then continue modifying each of them. This will ensure centering. Ensure adequate clearance between the gearbox and the screw head (s) by using very small screw(s) say 3 mm or less. A small enough countersunk flat head screw should be flush with top of the driver. ONLY RETENTION IS NEEDED, minimal torque is needed to drive the speedometer. You may need only one screw. And then reduce the outer diameter of the driver to 62 mm (same as hub).
Good solution:
You can cut 2 flats into the hub. Then you can use my driver.
But that defeats the intention of a drop-in installation (no modification needed) and makes it more expensive.
Good Solution:
Swap out hubs. Relacing and trueing a wheel isn't fun.
Not really viable solution:
The stock driver doesn't even fit the rotor. Too much cutting of the rotor and/or the driver. You would need to remove a lot of material and it still might not work. And it probably wouldn't look good. This is the main reason that I created my replacement drivers.