Rotor thickness minimum 4-piston KH?

I was in the automotive repair industry for over 35 years and we serviced thousands of brake systems since the seventies. What should be done and what people sometimes get away with are different discussions. Both rotors should be the same thickness to have equal heat expansion. Doesn't matter what caliper system you have. Just like both front drums should be the same specs. Braking is all about converting motion into heat. Rotors are inexpensive and very important safety items. Like having a bald tire on one side and a new tire on the other. When you make a hard stop, traction will not be equal. Be sure to flush all the brake fluid from the system at least every brake service with new un-opened containers of brake fluid. Drum and rotor specs are always cast into them. Back in the sixties some drums were manufactured thicker and could be machined up to .090 under size. This was also normally cast into the drum. 2 most important safety items on any vehicle are the brakes and tires. Everything else is less important.