I don't know the answer, but I do know that the '80s-early 90's Ford speed controls had a little pickup unit which went behind the dash. It was used in the add-on speed controls as well as some factory units.

The speedometer cable is unplugged from the gauges and stuck into this little pickup, then a second, shorter cable is attached from the back of the pickup to the gauges.

My guess is the number of pulses is not so important--the cruise control works by counting pulses per time, and maintaining that count. If the pulses are way off, I could see it refusing to engage because it thinks the car is too slow or too fast (most systems won't engage under 25-30mph and some won't engage over 85-90).

My guess is they're pretty close.

For my Amazon, I'm going to be using an early 1980s Ford dealer add-on unit, they pop up on ebay from time to time for 35-40 bucks.

This unit has the buttons on the turn signal stalk, which goes to a metal post. This metal post can be adapted to take the place of the stalk on the 122 turn signal switch.

Then it's just a vacuum source and a hookup to the throttles on the Volvo, power, ground, and that little pickup behind the dash.

Ben