Not enough information, JEQ. All we know is that it's a Chevy 396. Which one? Original HP rating?

Cams don't stand alone. They need to be matched with the carb, intake manifold, heads (including valve size and compression ratio), exhaust system, transmission and gearing. If you get a mismatch, you end up with less performance rather than more.

Talk to Comp Cams. Tell them exactly what you have. Ask what the 305 will do in that setup.