There is a performance gain with a proper multiple carb set up. It won't compare with port injection but that doesn't matter to most of us. The most carbs I ever ran was a 3 side draft setup from a '54 Vette on a 261 in a '40 Chevy pickup. The engine was not a race build but pretty strong. If there had been 1/8 mile drags back then I would have been famous. I've run several 2x1 setups and one 2x2. They all ran better than a single 1 bbl carb. I had a 2-jet on a 270 that ran very well. The coolest looking is a 3X2 Harper, and probably the most complicated.
I have always liked Zenith 28-228 with the adjustable main jets. They worked for me and are very adjustable. They have replaceable different size venturies if you can find them. I had a pair built a while bace for a 153 Chevy 4 cylinder I'm building for a roadster. They came on a lot if GMCs & International trucks. As for size you just have to do your homework and remember that most modern carbs are calibrated for V8s. Oh, The 270 I'm running now has an Edlebrock 4 bbl. It works but no cool factor.
