IF you're considering replacing the carb, CONSIDER using EITHER a 2 BBL Stromberg WWC3 or A Carter 1-1/4" BBD as used on a 1967 LA 318 engine. The air filter housing base is flat and the carb uses a bale assenbly with the wing nut to secure the entire air filter assembly to the carb's mounting flange; there is a rubber gasket to seal the filter housing assembly to the carb's flange and uses the standard pleated paper filter. The two carbs noted have a slightly larger venturii for more air flow but have the same 1-7/16" throttle plates. Your 273" engine will like the additional air flow. Everything resembles the original equipment if this is an important consideration. Just my opinion of course.
BOB RENTON