Year, make, model & whats the number on the AFB???? The carb. number is below the right front bolt that holds the carb. onto the manifold. The base needs to be in reasonably good condition & NOT eroded away from exhaust corrosion. I would take the AFB over a Rochester 4Jet unless your talking about a Q-Jet. Depending on application aftermarket (Edelbrock) can create problems with the kickdown/switch pitch hook-ups. For a Q-Jet, if you don't already have one, you will need the one yr. ONLY Q-Jet spread bore manifold. They can be costly being one yr. only. The ONLY carb. that will fit the manifold is also a one year only carb. You CAN use another year Q-Jet but you have to make modifications to the throttle shaft. Then you again run into kickdown/switch pitch hook-ups. Average is, depending on condition, $250.00-$500.00. Then with a Q-Jet you CAN'T use your stock air filter housing. Lots of things to consider if swapping over.
Send pics of the carb. & base.
Tom T.