I heard you could not do this as the pedal rod may not fully seat inside the mc.
I have no idea if this is accurate, but I need to bleed a completely new brake system and I'm reading all kinds of opinions, from bench bleed out of the car, in the car, open all calipers/cylinders and let gravity fill the system first, to force fluid from the calipers/cylinders side into the system as air rises.
