The WW2 jeep used an oil bath air cleaner assembly. It was purported to be a very efficient unit.
The air cleaner consists of parts F, G, H, K and J as pictured above. The filter is pretty symbol to install and use. Oil is poured up to a certain line marked on the air filter cup (H). A modern change to the oil bath is a dry filter cartridge insert. The dry filter replaces air filter element (G) and also includes an adapter to mate the dry filter to the assembly. No permanent change is affected to the unit. Anytime you wish to go back to slopping oil about the jeep engine bay–you can!
Over the course of the last 25 years or so there have been a few different dry filter “kits”. One was sold by Willys Minneapolis when it was owned by Louie Larson. The adapter was designed by Ray Cowdery (the guy that wrote All-American Wonder). This is the air filter cartridge and adapter that I have used for nearly 25 years. The cartridge used with this setup is the NAPA 2036 or WIX 42036.
A good friend of mine, “Brother” Callahan designed a replacement adapter in plastic when he couldn’t find one made of steel, like mine. He made a few and sold a few but it there wasn’t much demand because the cost was just too expensive for the plastic, never mind the cost of the machine work. These were machined not vacu-formed. So after making a few of these and not having much luck recovering costs, Brother stopped making them.
Along about the time Brother ended his projector a really sharp guy going by the name Fred-D discovered that you could easily “make” an adapter by buying two “doughnut rings” used in the plumbing of a toilet. One went under the air filter and another went on top. He said, “…order two Sponge Rubber toilet bowl rings P/N 2793K81 from McMaster-Carr. Phone # 404-346-7000 . They cost $2.71 each…” That’s a whole lot cheaper than any of the two earlier methods.But why would you want to stop using the oil bath filter? The dry filter is just a little more efficient at removing dirt and grit from the air. The dry filter won’t spill on your fender and leave a nice mess on a painted service that absorbs oil. On the flip side your jeep won’t be as it was. It’s really just a matter of personal choice.