So what oil SHOULD be used with a new engine AND why?

So what oil SHOULD be used with a new engine AND why? Here's the thing-my old engine builder said to use straight 30 weight non-detergent oil: The engine builder I have now said to use whatever you would normally use. In the book by Larry Sheppard "How to build a Small Block Mopar".he states to use either straight 30 weight or 15w40. I bought Wolfs Head straight 30 weight non-detergent oil but it says "hydraulic and compression oil" on the bottle with no combustion engine references. It's 80 degrees outside =do you think this oil is ok?
I have ALWAYS used a Pennzoil oil with ALL my engines and have never had an issue but finding a Pennzoil in straight 30 is next to impossible,btw.....
The new engine is a performance engine,big hydraulic cam,aftermarket pistons,etc