Okay I put in good stock mass air that Jeff at Mustang Specialties loaned me to test with.

Results, car did not like it. Check engine light came on and stayed on the whole time, idle dropped down to 500 then surged up to 800 and would not stabilize the entire time I let it run.

Switched back to the the larger Pro-M and added a new screen to it (wasn't running one since it had been damaged during some earlier re+ re) and the car started and went to steady idle around 800 as before and no check engine light. Likely after 10 or 15 minutes it would have come on.

I guess with the E-cam, Edelbrock heads and GT-40 intake it likes more airflow. So I think I'll look at a new 24lb calibrated mass air and put my 24lb injectors in.