I did a 2 bbl Rochester for the local dirt track car I sponsored. This as a 2bbl class, 500 CFM Holley was legal, but the guys I sponsored were very low bucks. I built the 400 Pontiac for them, used a iron Q Jet manifold with adapter to the 2 bbl. Car was a 76 X body olds omega.
I used a hole saw in a drill press to open the venturi's on the main body, the size escapes me since it was 25 years ago, but I took it out as much as I could without breaking through. I used a brake cylinder hone to smooth, and blend the inside of the venturis.
Die ground the clusters to remove as much as possible. I tapered the throttle shafts round end upstream tapered to a thin point on the bottom. I also modified the cross piece that the air cleaner stud screws into, but you have to be mindful of how much you take off, so as not to make it weak. I rounded out the square edge on the top of the air horn to help out too. Used a GM air cleaner base with an open element stacked 2 air cleaner elements to keep the restriction down.
He won a bunch of heats and features over 3 years with the combo, against a lot of chevys that had a lot more money in them, and they had the 500 CFM Holley too. I feel for how much money was invested, he did very well.
It's entirely possible to upsize the Rochester 2 bbl at home with basic tools, just requires some work.
I probably wouldn't sacrifice good tri power carbs, find something else, and keep the real ones as is.
