You will have to replace the intake manifold to use a 4 bbl. Stock intakes from 350's are plentiful, you can also go with an Edelbrock Performer intake, it gives better air flow than stock, raised my vacuum 2". You can usually get a used one in the $50 price range. For a carb 500 to 600 cfm will be a good match. You can go with a Holley or Edelbrock with vacuum secondaries for $220-250 for a factory rebuild. You can also go with the quadrajet and mechanical secondaries, which will get you better highway milage, but the Rochester q-jet used a poor quality metal in their castings, which wears around the throttle shaft and leaks. Edelbrock makes a new q-jet, but it's around $450.
