I don't use cheap alternatives. Go to ebay and plug in 'ford tractor air cleaner' and you'll get a list that has about a half dozen 8N air cleaners mostly used, some restored, and one or two new. The one Royse shows is the UNITED style with the rounded cup. DONALDSON, with the square cup, was used in '48 and after '49. The unit contains a wire mesh screen that can be easily removed and cleaned or replaced new. Simple. HINT: when working with the air cleaner and carb, use a lot of WD-40 around and inside the two rubber hose connections to help the rubber become more pliable and easier to maneuver off and on the tube and carb inlet. Pry the hose end sup slightly with a screwdriver and get the spray inside and around the perimeter of the steel tube and carb inlet. Use caution and patience so you don't rip the rubber hose. Then you'll need to buy new hoses.
Tim 'PloughNman' Daley