... I wonder how the factory broke cams in, did they really rev their engines for so long 2,000 times per day?
Just an aside in your conversation; yes, they did. Touring a Ford plant in the carb'ed flat lifter days, they did the startup at the end of the build to check for leaks, etc. This was at high idle, and a tag was then placed under the throttle to raise rpm during warmup. The cars slowly moved along the line, humming away at slightly elevated rpm, towards the final check station. By then the cams were broken-in, and they were idled-down, checked for timing, idle, and tested for emissions. Out the door.
The rpm for cam break-in is generally suggested at 1500-1800 variable, which is not much above the choke's high idle, so it doesn't take much. Today they do break-ins at the engine assembly plant, not for lifters, but mostly to seat the piston rings with dyno loading. Rings need to be seated within 20 minutes of first start with high load and rpm for best cylinder seal and engine longevity.
PS: If blkfrd doesn't mention it in his answers, I would also add a good magnetic oil drain plug to help catch any remaining floaters before they embed into your soft bearings.