So is this saying the seat belt thing only applies to federal vehicles or it was a federal requirement?
It was a federal requirement:
This seat-belt interlock somewhat crudely, prevented the car from being started unless all front-seat occupants buckled their safety belts first. With only a six-month lead-time, the National Highway Traffic Safety Administration (NHTSA) mandated the device for all 1974 model cars in the U.S.
The interlocks didn't work well, and were not required in 1975+
The unseemly haste of dictating a huge change in American motorists’ habits prevented a reasonable, normal development period to “de-bug” the gadgets. The result was that grandmas, grocery bags and guard dogs alike triggered the no-start unless the belts for the front seats they occupied were fastened first. Plus, people rejected the Big Brother attitude of forcing them to buckle up before they’d bought into the notion. Back then, only 10 to 15% of occupants buckled up; today it’s up to nearly 100% in some American jurisdictions for front seats.
A huge outcry quickly arose. Frustrated and indignant citizens bombarded Congress to complain about the devices, and our representatives quickly passed a law outlawing the interlocks.
I can't imagine that a police force would require their officers to go through all those hoops to start their car. Surely every cop Monaco in the country had this disabled quickly after it was received from the factory. In the bluesmobile universe, I think it was disabled long before Elwood got it.
I'm surprised Chrysler wasted their time putting them in police package cars but I guess they had to meet federal standards police car or not. As you said I'm sure they were disabled, that could cause a life or death situation for a cop.