Can those of you with big engines (500CI range) tell me what your idle speed is and the duration of the cam you are using?

I'm putting together a 500 inch engine and I'm trying to decided on duration atm. I'm leaning toward the mid to high 240 range at .050 but would like to hear your comments on the subject. This will be a street driven car so I'm not looking for something radical. I know big engines tend to make big cams seem smaller so I need your input and advice.

Car is a 1966 Cutlass with a TH400 Switch Pitch (1500-3200 stall), CNC ported Bulldogs with lots of CFM (I have the numbers if interested)

Thanks,
George