Looking for so help. I have a 4 Galaxie with a 390 with 406 heads and a 63 dual quad manifold. Several years ago i installed this engine replacing a 352. At the time i installed 2 Holley 450 carbs. I did not know what they were when I bought them. After research I find they are better suited for a high winding small block with a tunnel ram and big gear. I have none of that. Car is a cruiser and yes I know it would run better with one carb but i like the look of two. With 450s it stumbled on take off real bad due to manual secondarys opening and not enough rpm. Other that that it ran OK and pulled down 15 mpg. I perched a matched set of 600s (naby years ago for a 428) and yes I know these are too bid although a buddy ran 2 600s on his 390 with no issues. I am not making a race car it is a driver. I just trying to get the jets close. Since r9834ebuilding the carbs and on its first road test about 3 miles it ran terrible, worse than 450s. 450s were jetted 20 sizes bigger than the 600s. 65s in the 9834s and 85s in the 450s. With the 600s it was backing firing out the exhuast at steady 55 cruise. I am sure the power valves need replaced. have 6.5 with 8 inches of idle. I would like to knock down the tear down time on jet replacement due to having to pull one carb each time for jet swap. Ok that was a lot of information and probably not nough. Help.Oh and it is a stock auto trans with 3.00 rear gear.