start by getting a vacuum gauge on it in gear, and making sure you've got a good signal. you should have probably 16-22" with this 'mild' cam in your engine. with that and a stock converter you dont need anything too big or exotic, you won't be happy with your engine guy's recommendations. not enough vacuum or too large a primary venturi, and forget about getting your idle mixture right, not to mention your transition, and main circuits. there are lots of ways to mask an oversized carb, they are all a pain in the ***-drilling primary plates, power valve sizing/timing, and jetting that is way off. try working with the carb you have now before you throw good money down the drain.
if your heart is set on a carb change, consider a holley street avenger. the first generation of these units had some issues, but holley has them worked out now. these carbs out of the box require very little adjustment, and this is good if you're not confident in your tuning abilities. holley even ships a dvd with their carbs now to help people set theirs up.
these are vacuum secondary, DUAL FEED carbs, not to be confused with DP's, with electric chokes-very easy to adjust. if this car is a cruiser, you will be very happy with the result. your mileage will slightly increase because the secondaries won't come crashing in the second you mash the throttle-they react with engine LOAD and DEMAND and will come in smoothly with the correct secondary spring.
holley has on their website, a "carb calculator" which chooses the best cfm for a particular application-check it out. and you should do some reading on how to properly size your carburetor, you'll see how easy it is to over-carb an engine and why.:grin:
