If you can get under there and clean the housing and cover, there will be numbers cast into the housing somewhere.
Also details of the breather, older 7 1/4 had a cover that sticks up slightly on the axle tube (not like the vent bolt that holds the brake distribution on 8 3/4" rears.) many times they are covers in dirt and grease so not easy to see
But please put the drum on the axle flange and take a photo from the rear showing the backing plate and the drum and how they engage each other
