If you are running the stock 318 valve springs, you should be fine with any reasonable quality 10w30 oil. Especially on an engine that is already broken in. The worst oil you can buy today is far superior to the best oil available when that engine was made. A 15w40 "diesel" spec oil might be a good compromise, as they tend to still have some zinc, and will help remove the sludge the old oil has certainly turned into. You face far worse damage by starting an engine which has sat for 4 years than by using a low zinc oil. Personally, I would pull the intake and valve covers, clean and re-lube the your cam and entire valvetrain. If the engine still has the original cam sprocket, I'd replace that now too while it's easy, but thats just me.
Yes, I understand the purpose of zinc compounds in oil, but I think the whole think is getting blown out of proportion. Zinc has been gone for a while now, and all of those flat tappet engines running around out there didn't suddenly self destruct following an oil change. They said the same thing about unleaded fuel, and engine life went up dramatically because of the lead removal. On a stock engine, or any cam that uses stock or near stock valve spring pressures, I wouldn't lose any sleep over it. That being said, if I was breaking in a new cam I would certainly use a zinc supplement in the break in oil. After break in, I would use the same synthetic I use in all my flat tappet engines (5w40 Rotella Synthetic) and not sweat it too much. Many cam manufacturers now recommend using a "break-in" spring or just the outer spring to keep pressures down while the lifters and lobes wear in, giving them a fighting chance with the low zinc oils.
