Best intake manifold and carburetor for a 273

I’ll be a bummer and tell you what you’ll experience.

Loss of low end torque
A gain in high rpm HP
Camshaft dependent, the two intakes will balance out around the same rpm area of approximately 4000/4500
You’ll pick up a usable 500 rpm up top and hang onto the power to 5500.

To make the most of this intake, a gear reduction and extra stall in the converter (and matching the camshaft of replaced) will help abate low end torque loss, get you into the camshaft power band quicker.
I have no low end torque and I have no high rpm horsepower with 2.71 gears, 225-70/15 rear tires and the factory single exhaust. I drive this car on the Interstate quite frequently.