Port my current M1 single plane or install the RPM Air Gap?

Personally I’d run with Ratbastards suggestion.

Your exhaust is TTI W/an X pipe?
This throws away low end torque. A pressure wave cancellation box should have been tested after the header for increased low end torque output.

Questions!!!!

What size tires are you running?
What is your overdrive gear?
What are your cruise RPM’s?
What model carb? (Mechanical or vacuum?)

At 422 cubes, getting a tic over 20 MPG‘S is very very good.
The 2.196 final drive ratio with the cubes and cam size, WOW!