To use two or three Rochester B carbs is a little bit of an exercise in patience. To get that kind of a set up to run really well requires a good bit of tinkering. Go on to our main site and find Pat Smith's outstanding article on how to set them up and you will see what I mean.
I generally had better luck using smaller carbs for like a 216 chevy (Carter YF for example) in a 2X1 or 3X1 set up.
Quite a few years ago now, Tom Langdon (before he retired from GM and before he took over Stovebolt Engine Co.) suggested that I try Ford Pinto Holley/Weber 5200 carbs. These are progressive two bbl carbs. Like a Q jet, small primaries, and progressive secondaries. I put them on my 235 and boy did they make a difference in drivability and clean spark plugs. I would think the same would be the case for a 3X2 install. You will need adapters and you will have to check hood clearance but you might consider those carbs. 1974 versions are the ones I use, those carbs have a threaded fuel inlet rather then the earlier brass nipple.
