Yep, try the 20w50. Or if you do not have hydraulic lifters, try just straight 40w non detergent. All the old 2 cyl. John Deeres manual says use 30w ND. That's the cheepo stuff, bet you will see a rise in oil pressure.
I don't know what the original manual says to use in the 1950's cars and trucks.
Like the old tractors manuals even say use 30w ND in the Hydraulic system. But people want to switch to all these modern oils and eventually have problems with foaming, ect.
Remember STP?
