I am pretty sure my 408 that makes 504 up will work fine with a 10 w30 or 5w30, but which one? It is a roller cam motor and held 60 psi at 160 degrees water temp after ten dyno pulls. 80 psi with more rpm, like 2500? That was 30 at break in oil. What additives do these motors need?

Myself... 5w20.. and see how it acts .. you
dont really need any additives with a roller

This is off topic, but which cam are you using? I'd like to make 500 hp with my 415, but I'm concerned about idle speed and idle vacuum since I'm running an automatic. Tell me more about your motor and maybe you can help me decide. Thanks!

The cam is a Comp muthr thumper, with 291 intake duration and 311 exhaust. It idled down to about 900. A call to Comp might give you some good info. Since you have a 415, I bet it will be fine.

Mike, you think something like Mobil 1 5w20 will be fine? I am guessing it is ok to switch right away, since it is a roller motor.

Yep... you'll be fine