back in the day I had a 383 4spd road runner. I tried different carbs with the stock intake (factory stock engine and exhaust); stock avs, 440avs, 780 holley, etc, and I can't say that any of those carbs that were larger than stock made much difference. i'd do the 650avs2 (nearly identical to a stock avs without the emissions hassle) on the stock intake and be done with it.