Engine air filter

The older ones do have a filter cartridge. If he's taking it apart I'd guess his does.

If you can't find a number, get the dimensions and match it up on a cross-over site. Pretty much every manufacturer has one.

If you find 2 or 3 with the same dimensions pick the one,with the highest CFM rating. Diesels like to breathe.

That’s pretty close to what mine looks like. I can’t find a number on it, I haven’t taken it off yet. I was going to order me a new one online and get it before I took it all apart. Thx for the help.

It should be printed on the filter itself. I assume, being a diesel pusher, it's the all-in-one cartridge type.

With these you don't just change the filter, you change the entire housing.
Something like this...