The grub screw will usually have a small hole running through it to allow some oil in case the filter gets plugged or the lines get kinked. There is no pressure relief built in to those old filters, and dirty oil is still much better than no oil. Besides, even that system is not a full flow oil filter since oil goes to the rear main before it goes up to those fittings.
Without the grub screw, you have all the oil (less what already went to the rear main bearing and into the back part of the crank) going across to the main gallery. The CMPs I have worked on take a small portion of that oil into the oil filter and dump it back into the pan.
I cannot say what was in use in late war vehicles, because the bulk of Fords in Canada are 43 and earlier. I don't see many 44 or 45 dated Ford CMPs around here. I think they were needed overseas. However, the system shown in the second photo you show I believe would have had a fitting that reached down into the hole and blocks transfer across to the main. If you blow the photo up much larger you can make it out. The external bypass looks like that used in the carriers. Again, I have not run into that in the domestic CMPs, but then again I have not seen it all.
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