I also have a 1981 Chevy Sportsvan. It didn’t has cruise control. I installed one of a blazer. They have a vacuum switch on the brake pedal. When you hit the brake, vacuum from the Cruise control diagram is released, so it don’t pull the throttle. It is a extra security when the cruise control isn’t disengaged by the electric circuit.
On my 1980 Chevy van, there is now vacuum switch. So probably you right about the recall.
Does your CC also have a yellow, bleu and white wire?
When I connect the yellow and bleu wire to 12V. And I connect the white wire for 1 second to the 12V, the cruise control is engaged.
When I connect the white wire to the ground. The CC is disengaged. But I did have a few times, it didn’t engaged immediately when I connected the white wire to the ground.
When I disconnect the bleu wire from 12V, the cruise control is disengaged. When I disconnect the yellow wire, the CC is also disengaged.
You can installed a relays, so when you hit the brake, the 12V is disconnected from the yellow wire. The cruise control has now power, and must be disengaged.
But when the brake switch is broken, you still have the possibility that the CC don’t disengaged and then you have a problem.