best type of oil for 71 340 engine

I'm running a 70, 318. It has all new gaskets and seals and is basically extremely low mileage. It was beautiful inside. I've run 5-30 Mobil 1, it seeped a drop or two. I switched to 10-30 for a while and had no problems. I use 15-40 Rotella now, I had a case given to me. I think the Rotella works fine and it has zinc so the new cam has given me no problems. Just make sure it has ZDDP (zinc) and 10-40 should be about right unless you have large clearances on the rods.