I have a 1950 Ford 8N tractor with 4 cylinder gasoline engine equipped OEM with a by-pass filtration system. My question, what is the correct style filter to use. There are 3 types on the market. Purolator offers a pleat style element, which I thought was only for full flow systems. Fram offers a stacked cardboard disc style, which I am unfamiliar with. FleetGuard offers a woven cotton string media, which I thought was the correct media for by-pass filtration systems. Your thoughts please. Thank you. Philip.