Which oil to use in reman 351w?

The only real benefit to using a synthetic is a longer time between oil changes. Even though it takes longer for the synthetic to degrade, it still gets dirty at the same rate. So I prefer to stick with conventional oil and change it every three months. If you want to use a supplement, can I suggest the car-quest brand "engine restore". I use to use lucas. But I tried the engine restore to free up a stuck lifter and it work in 5 seconds. I love this stuff. If it will free up a lifter that fast, just think about how much friction it is cutting out of the engines other moving parts. Use a good oil. I use quaker state. I belive your engine would run best with 10W-30. I think 5W-30 might be a bit thin for that year motor.