As far as switching the cruise control feed from the Ford MAP sensor to the stock VSS signal, would it be possible to adjust the pulses from the Ford sensor to be closer to those of the vehicle's VSS sensor pulses? Looking online quickly, it seems that you can halve the frequency output of a device by using an IC such as the LM 555 or LM 556. If the frequency could be halved, it would be possible to go back and forth between a cruise control set for MPH or MPG without the vehicle's ecu thinking that something's wrong...
Just a thought.
Also, there's a PDF available on Rostra's website that has information on VSS pulses per mile for cars from 1986 to 2007.
Rostra Precision Controls, Inc. - Technical Support