Friend of mine who was a Kawasaki nut in the early 80's bought a late 70's Kawasaki that was a "police bike". He said he had contacted the factory and the police bikes contained "heavy duty" parts, usually brakes and some other assorted chassis parts that frequently seen high usage from police departments. He said the person from the factory referred to police bikes as the "John Deere" version of the KZ1000, meaning it was built to be as reliable as possible. If i remember correctly, the engines were stock.
I did some road racing at a local track with a 77 KZ 1000 and they were pretty bulletproof. Handling was on par with that era which, compared to now, was horrible! I ran the crap out of that KZ, track time a lot of weekends, daily rider the rest of the time. Castrol GTX motor oil from the Air Force Service Station at like 60 cents a quart. Changed the oil every 1500-2000 miles and when i sold it @52,000 miles it ran very well with virtually no oil usage. Good bikes.