Wow, no reason to turn this into brain surgery. Bolt the bigger carb on and adjust the idle mixture and idle speed. Take it out for a healthy flogging paying attention to bogging or backfire. Pull off the road and pull out a few spark plugs to read them. If the carb is too rich they will be black. The engine will only pull as much air/fuel as it can. Just because the carb is bigger than that number doesn't mean it's a bad thing or that it won't work. . Proper jetting is the key, all up to a point of course. (no Dominator on a stock 2 barrel 273) @318willrun ran dual quads on a stock 318 without issues.
