Originally Posted by 403_CHEVY
i'm from cali, the engine is still stock right know and it's gonna be going in a 1980 chevy scottsdale
First I have to say I'm not 100% current on California emissions regs. When I lived there you had to meet regs for the vehicle or engine, whichever was newer. I understand that has been changed to year of vehicle only.
Your '80 Chevy is not exempted because it's not yet 30 years old so let's assume you have to meet 1980 regs. Depending on what part of the state you live in you have the annual or bi-annual smog check. To pass this you'll have to not only get by the sniffer but also the visual. That means you'll have to have in place and working EGR, vapor canister, catalytic converter, PCV, etc. Also any aftermarket parts will have to have a CARB number with documentation.
All that being said you should be able to get 300hp with a good intake, 600cfm carb, mild cam, headers, and probably a quick polish on the heads. I can't give you much in the way of specifics as again I'm not sure what is legal. Keep in mind a 403 isn't so much a horsepower engine as it is a torque monster.
Another quick point. I hope you got a transmission to go with it. The BOP bolt pattern is different from a Chevy and I've never seen a Chevy truck come with the dual bolt pattern bellhousing. Good luck.