For the fact it is a flat lifter and not a roller then I would use any diesel grade oil in it. Thats what I run in my dad's 29 GMC truck. It has the extreme pressure treatment in it and it helps to prevent cam wear from the oil being pressed out from between the cam and the tappets for those who choose to be correct on parts names. so I run 10w30 diesel in all my vintage cars and yes even in my 9N Ford Tractor.