Mark, The pic you are referring to is my own tractor and yes it is a diesel so you are right about that.
But the original tractor that MikeAC asked about is a gasser.
You can see the photos of it by clicking on the link below.
As for the air cleaners, as far as I know all the 65-75 3 cyl gassers had a paper filter with the cover in the left center hood and all the 65-75 3 cyl diesels had an oil bath - serviced through the grill. Exceptions were some of the pre 75 Utility models like 3400, 4410 and maybe 4400. On those the diesels had a paper filter accessed through the Left side of the nose.