has anyone ever used one of those carb adapters to adapt a 4 bbl to a 2 bbl intake? i know preformance will suffer but i have a chance to buy a 600cfm holley at a good price and i want to be sure i'll get improved preformance from it first.

 

You would not notice much of a difference by adding a 4bbl intake and carb let alone putting a 4bbl carb on a 2bbl intake. I don't think they make an adapter for this and if they did I would almost guarantee it would give much worse performance and gas mileage than your 2bbl. 4bbl manifolds are a dime a dozen in the junk yards so if you are going to do it I would do it right.