I just had an idea on how you could accurately drill a hole perpendicular to a flat surface: Loosen the tilt adjustment of your drill press table and rotate it 180 degrees, so it is upside down. Then hold or clamp the carburetor flange up against the table surface and drill down into it.
Here is another idea (that I have actually done): to tap accurately, mount the tap in your drill press, and remove the belt. Then rotate the driven pully by hand to rotate the tap, as you gently lower it into the work.
Doug