There have been 2 popular filters used on these. The dealer installed filters were AC. The aftermarket were Fram. The Fram cartridge number is C-4. I don,t remember the AC. (50 years ago) number. The Ac uses a 5/8 wrench on the cover bolt & the Fram uses a 7/8 or sometimes has a big wing nut. Any parts store should be able to come up with a cartridge or the specialty stores have them. The specialty stores usually go by diameter.
