Here is my 2 cents: break-in oil is still in engine, correct? Continue using that without beating on the truck
until 1000 km (almost 500 miles). Then change oil to good quality DINO oil 10W30. I personally would
add in some Marvel Mystery oil and ZDDP additive to be on the safe side. I know you went with the roller
camshaft, but there are many other points in that engine that have sliding friction that could benefit from
those additives. Use the 10W30 for another 1500 miles, and then you can change to synthetic or synthetic
blend, if you wish. From then on, depending how much mud racing you do, change it every 3000 miles.
The newer oils marketed for extended oil changes (5000, 7500, 10000, 15000 miles) do not apply to you!
Those oils are for the newer, computer controlled, fuel injected modern engines. You can't just pour one of
those oils in your old-school BBC and think you don't have to change the oil for 15000 miles.