...For stopping power, the 911 RSR used the same ATE 4-piston brake caliper as the ones found in the 917K https://pbase.com/917carl/image/26810376 and https://pbase.com/917carl/image/26810381

Note the large cooling-fins (cross-fin) incorporated in the caliper including the 'bridges'. While talking about the cooling-fins, I'll like to clarify that the 1973 RSR had "vertical" cooling-fins and on the bridges as well, while the 1974 RSR had "horizontal" cooling-fins and none on the bridges. Take a quick look at the unique 'parking-brake' system using a 'clam-shell' design around the brake rotor instead of the more common drum-brake setup of the street 911 https://pbase.com/image/53177198. One last thing, the pistons on the front calipers are much larger than the pistons used at the rear and a quick way to identify the front from the back calipers.