I took some carbs to the flow bench for testing. And this is what we found.

So the test is done.

Test plate with 1 1/4 " hole = with a clay radis = 153.3 cfm at 28

40H carb = AJ 33A = 68.4 cfm at 28

300 carb = AJ54AT = 70.8 cfm at 28

Also tested a N-2150S carb.

Test plate with 1 3/8 hole = with clay radis = 197.4 cfm at 28

20H carb = N-2150S = 94.4 cfm at 28

A 40ci motor needs 72.049 cfm at 7500 / 2 = 36.0245 cfm
A 40ci motor needs 76.853 cfm at 8000 / 2 = 38.4265 cfm

So,we are good to go with the carbs on the 40H! They will not hold back the motor.

Just FYI.
Randy