I run Amsoil Z Rod 20w50 full synthetic. It has the zinc additive which it necessary for the flat tappet valve train in these engines. It maintains great oil pressure even hot at idle. Kinda pricey but when only changing oil once a year its worth it. That and a Wix filter.
I also use Shell Rotella 15w-40. Yes, it is a diesel rated oil but it is fine for gas engines, too. Since I have an F250 Powerstroke (4 gallons per oil change!) and 2 Alfas plus a motorcycle, it is simpler for me to use the same oil in everything.