[tubman]

Welcome to "The Barn"! Regular old 10-30, unless the engine is completely worn out and needs more. These old flatheads have much lower valve spring pressure than the typical OHV engine, so you don't have to go nuts buying oil. One thing you should be aware of; I don't know about trucks, but the manual for my '51 club coupe says to do a chassis lube every 1000 miles! I have the chassis lubed a couple of times a year, and one of those times. I change the oil and filter. I think a lack of maintenance is the primary reason for people complaining about the front suspension problems on these vehicles.