I sounds like the air cleaner type was a product improvement, and that is was to be retrofitted onto the earlier transfer cases to replace the simple tube and cap. But in all seriousness, for the miles any of us will put onto our vehicles, nor the dirt we will subject them to, the nipple and cap would likely be fine.
If you are talking about the little nipple and cap on the jeep transfer cases, they are normally spring loaded onto a little check valve which will build up pressure to about 3 or 4 psi before reliving the pressure. They are usually 1/8 npt thread so would be pretty small for this application. However, with some bushings, it would work fine. The same nipple was used on the M35 deuce (and a thousand other vehicles) for that large transfer case for the last 60 years.
Edited to add: I had to look up the early Jeep transfer case breather and just saw that some indeed are a nipple with small cap retained b a cotter pin. But some sources are showing the pressurized cap which is more what I am used to. Someone with a WW2 Jeep will have to confirm if the nipple and cap type is 1/8 NPT.
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