I cleaned the filter on my D2 recently. It was similar to yours. I soaked it in gas for a few days then hit it with the pressure washer and did a pretty good job.

A hot tank works the best, dont steam clean them, I took mine to the Cat dealers hot tank, turned out good and clean.

Hi Mike,
the scans below from Service Magazines of the day tell us what not to do when cleaning the non-removable screens in the oil bath air cleaners--one of my jobs at the Dealer in early days was to use the air ring kero tank before steaming them out thoroughly.
Today's de-greasers likely would work OK if the unit was set upside down with the rectangular clean air exit blanked off with a suitable plate and left to soak with a bit of shaking agitation now and then.
Cheers,
Eddie B.

Thanks so much to you all for the replys, Ill cap it off and soak it in Kero. I cant thank everyone enough for the help, Im ready to get the pony assembled and then my buddy will get it painted,
I want to get it painted before I put it back on.                                                                                                                                                                                                                   

Just wash the screens in solvent. catskinner

Thanks for sharing Mike. Very sorry to hear of the loss of your brother and his wife. I'm sure they would be honoured by the work you are putting into the old tractor that you guys all worked hard on to make a good living. Keep the pics coming.

I have been on a journey to try to track down my grandpa's Cat D4 7U series up here in British Columbia but havent had any good leads despite Facebook and other classifieds in search of. I have another 7U that I will try to set up as my Papa's was in memory of him. I have a friend that will deal me a fender tank, levers etc...to convert it to how my Papa's was.

Looking forward to following along.

Mangoman

The "helper" on the tank is my late Dad, John Sihlis with my Papa, likely the day he took delivery of it around 1955. 

Nice photo's there Mangoman, sounds like you have a nice project ahead of you too, has the fuel tank on that D4 been crushed on the side, because the paint work looks all shiny?

Yes Mike my Papa bought the tractor second hand but it looks like it had a fresh coat of paint when he bought it a few years old. Funny how that tractor had a caved fender tank from when it was young and I have a '45 5T that was a logging Cat all its life and the tank is straight as an arrow 😁

Some "operators" used all sides of the tractor when working in the woods.

Rome wrote:

Some "operators" used all sides of the tractor when working in the woods.

we always called those guys tractor drivers in a derogatory kinda way