The GMC CCKW

I would like to speak about a important thing: 1)The two holes of master cylinder filler plug cup,for a better functioning of it.2)The incoherent thing in TM 9-801 April 1944(page 41) manual that says the crankcase oil level should be kept to FULL mark,showing at the same time the arrow between the FULL and LOW marks.In the same manual(page 90) says in the picture nº 1 that the oil level should be UP to FULL mark.What do you think about this two objects?Regards.

I'm thinking that the master cylinder has "one vent hole" i would think if it is not clogged up this would be enough thousands of GMC cant be wrong , as for the oil level between add & full is the operating range on a new "to me " truck i always change the oil as per the Manual and then check the dipstick and that is my starting point . Remember someone might have switched dipsticks . Hope this helps .