It is possible to use car brakes or even air plane brakes as the brake for a dyno.
For smaller engines such as kart engines you can run one rotor/caliper setup, or for more powerful engines you can put many in parallel such as done here. Run the engine at max RPM and gradually push the brake pedal until engine RPM is below the interesting area. The brakes heat up pretty fast. Add fans and don’t run long runs if you have heat issues. In any case a run does not need to take more than 10 seconds or so. The calipers will need to be kept from rotating by the load cell. Pretty simple setup!
One drawback of such a setup is the difficulty of accurate brake control. It may be possible to use a servo or stepper motor to somehow modulate the brakes, but it is not straight forward. An automatically controlled brake dyno will be more repeatable.