I remember very distinctly the first time I was ever around when a Motor was broken in. I would have been some where in that 7-10 years old area. My grandfather had just finished putting a blown 408 in a 55 belair. He used a drill with some home made adapter to pressurize and prime the oil system, set the timing close to where it should be, dumped a pop bottle cap full of fuel down the carb, and had me hit the key. As soon as it fired he took over throttle control, and tinkered with it till it had a high idle. After that he just played with the throttle up and down for about 20min, shut off the car (I didn't realize till many years later that he was breaking in the cam), changed the oil, set the valves, fired it back up, let it get up to operating temp again, did his final adjustment on setting the distributer, as well as setting the carb for the proper idle, then said get in.
We proceeded to do about a 2 block long cooker, drove around town, out on to the hiway did a couple more full throttle pulls, came back to town, put fuel in the car, went back to the farm, changed the oil again, and he pulled the plugs looked at them and changed them out. That was it.