I've ran and broke in several new cams in Mopar SB that I had rebuilt by using 4x4 under the front of the oil pan and under the front of the 4 speed tranny, I would hook up a complete stock exhaust system to the mufflers with no tail pipe and run them until they got up to a little over 200F on a mechanical water temp gauge and then shut them off and let them sit to cool down until they were below 160 F and then run them again until I got 30 minutes total run time at or above 1500 RPM, sometimes, depending on the time of the year, I would have to run them 2 or sometimes up to four times to get the 30 minutes total run time.
I would use a stock 1970 SB radiator without a fan and no alternator, one short belt that I could force onto both pulleys that would slip a little but would spin the water pump pulley fast enough to circulate the water with no thermostat
i did 4 or 5 different motors that way
I wouldn't try that on BB or Hemi motors, I would break them in the cars they went into or on the engine dyno testing and tuning them