Stock engine means flat tappet cam which will like/need zinc. Diesel engine oil like Shell Rotella T has it. It is available in 10W30 at Walmart. That's what I would start with. If hot oil pressure is low (below 20 lb) step it up to 15W40. There are lots of other choices but I like the convenience and reasonable cost of the diesel oil.

Note Mobile 1 in standard car grades does not have much zinc. The 20W50 does but is probably higher viscosity than what you need.