An article I did sometime back on oil for these motors:
Nicks Modular oil article
I had some long conversations with a GM powertrain engineer that worked on the Corvette oiling system. His basic answer was diesel spec for everything you care about because of the higher additive levels. Local fleet program I get all my PI head cores from use 15/40 diesel spec in all their vehicles, and I have seen MANY 500,000 mile heads with zero wear in the cam bores. Those heads at 500,000 miles make typical 50,000 mile Mustang and truck heads look like junk.
Since I live in Florida I run straight 30W diesel spec year round in just about everything. If I lived up north I would run 10-30 diesel spec since you can get it easily up there. It doesn't matter whose name is on the bottle anymore these days thanks to the EPA.