I have had Little Willy for a few months now and one thing I found was that the shiny green oil bath Donaldson air cleaner was missing its oil bath. Hence it was not filtering anything.
I struggled to confirm it was an FAE07 and then struggled to find the oil bath and screen. I would have liked to have kept it.
Then I started looking for a replacement and here it is, a Donaldson G070020. Brand new it is a 7" diameter filter (same diameter as per one fitted in 1951). It has two stages, the first one uses inertia and changing airflow to dump dirt (much as an FAE07 did, but it is self cleaning through a hose) and then there is finer filtration through a paper filter suitable for a more modern or diesel engine.
The capacity is around 400cfm and it will filter finer than an oil bath (not that it needs to). It is oversize for the L134 but should give years of service.
The only drawback is that the outlet looks larger than the 60 year old one and it is clearly not period correct (but filters the air).
Cost was only $80 plus shipping.
If I find an oil bath I will put the old one back on and use this for my J20.