I would think a Tri-Power/Six Pac is better on the street than a dual 4 set up. Mopar, and some Fords did pretty well with them. Especially the 435 HP Tri-Powered Corvettes that was in production up until 1969.
While not in stock forms, I have both sets up on cars in the garage right now. A all Edelbrock dual quad set up on a 350 small block in one car and a tri power set up thats an offy manifold with Rochester 2GC carbs on a small block. Street wise the tri power is hands down better. The dual quads tend to load up more often in traffic. The tri power also gets better mileage. The dual quad is only slightly better at WOT. The tri power works better on 327 and smaller small blocks I have found. Dual quads work good on the 350 thats got alot of speed parts. You need to go out and open the dual quads up more often than a tri power setup.
I agree with JohnZ there were 3 duce intakes for smallblocks made by Edelbrock or Offy. There was one with 2GC,s on Graigslist around here a couple years ago for less than 1K. I thought about it but the carbs were all regular 2 barrels, but probably should have got it anyway. I think GM banned multiple carbs except the vette after the 1966 model year. Up to 66 pontiac and Olds had tripower since the 50,s. The chevy 348 also had tripower until 1961.
Yes GM banned multiple carbs after 66 except the vette in terms of production line units. Most of those aftermarket tri power intakes are setup for the 2GC's, but they also made them with Stromberg carb bases as well, but you dont see it much for Chevy engines, you only see the Stromberg bases when you are dealing with 4x2 and 6x2 intakes. With those SBC intakes you would go a take the carbs off a 348 setup to use as they were already ready to go. They run really good on the 348 motors.