But, the oils were different and the factory had a way of running-in engines before they hit the frame rails, back in the day!
Being a stock rebuild with very little valve spring pressure, shutting it down to tune probably is ok, BUT you really should run them as is for the 20 minutes as long as it's not hurting itself or overheating. In my mind, a little out of tune is OK, and you can always do simple, on the fly tuning to the carb and timing without shutting them off. New camshafts need oil on the lobes, and the only way it gets there is from being thrown off the crank and rods, and each time it is shut down, the oil drips off and you have to start again.
There are a thousand different ways of starting a new engine, if it still runs when you are finally ready to go for a drive, then your way worked, if for some reason it all goes bad, your way didn't work..........
Joe
