If you are running a comp cam they have oil just for break in. Follow the instructions with the cam I believe it's 1800 to 2200
Rpm for 20 minutes varying the rpm but double check me on that it should be in the cam installation instructions as for weight I have used
Straight 30 weight in the past for break in. After the initial break in run change the oil if it a street motor I would not use synthetic at the first change put a few hundred miles on it and change it again and use what you want as far as synthetic goes. I am not saying comp oil is better than joe Gibbs it just what I have used for break in before.