When I installed an Equus 9000-B on my '85 manual, I had the choice of
magnets or a wire to the coil.  At the time, installing magnets seemed
like an unnecessary step so I opted for the wire to the coil and it has
worked perfectly for several years.

The only difference that I can see is my speed signal is RPM dependent.
  If I have to downshift it kicks the cruise control out whereas magnets
would see no difference in axle speed.

If I have to downshift, I don't need the cruise control engaged anyway.

Mike
Houlton, Maine