Keep in mind that engine will have nylon timing gear.
Having owned an 89 dodge ram with a 318 which I drove til the wheels basically fell off,putting in excess of 450000kms on the engine using the cheapest oil available(pre-bitog,pre-20s) I can assure you oil choice isn't a big deal. Just make sure there's oil in it. The engine was never opened up and ran like a top but the rest of the truck was toast.
My second 318 was in a 95 or 96 ram,which was driven to hades and back,twice,and was t-boned with in excess of 450000kms as well,with a great running engine.
Again I wasn't much of a maintainer at the time,beer was more important in those days,so it got a steady diet of the cheapest motomaster oil I could find,yet it still ran great when that lady ran the light and smoked me.
I'd go a bit thinner rather than thicker,only in an effort to reduce the strain on the nylon gears when cold started,and toe in to the throttle gradually instead of just flooring it to prevent the nylon gears from failure.
If you don't drive it line a race car I'm sure it'll run for nearly forever.
What transmission?
That's the only thing I ever had to fix on those 2 dodges,was the trans,on both of them,well and the rear end on the 89.