Wood, no offense meant but how can you be sure of that?
If you are sure, then surely you must know what that thing is, and therefore have a way to cross-reference the air filter.
Unless you're running your tractor a LOT in some pretty nasty conditions, you're wasting your time and money replacing the air filter every year.
Heck, I grew up on a farm and we NEVER replaced a single air filter in 30-odd years. Dad pulls them out and blows them clean with the air hose occasionally, but I can't say as I've ever seen him spend money on a replacement filter. These are tractors that got run 200-300 hours every year in dusty conditions... Not so much now since he's downsized the operation and upsized the fleet with a bunch of old Farmalls, but still...