I use 20w/50 w oil. Your biggest concern is to make sure the oil you use has high levels of zinc in it. The only affordable oils I have found locally that still have zinc in it are Valvoline VR-1 racing oil and some Kendell GT-1 oils.
If you can locate a place to buy it, Brad Penn has a high zinc dialkyldithiophosphate content oil. (Previously a Kendall refinery in Bradford, PA.) I’m running Brad Penn in a few of my cars now. http://www.penngrade1.com