air injection ports

went through this exact same thing. i have a 64 dart with a 360 so it was real tight in there but we took the headers off and lifted the motor up an inch or two and that was just enough to get an air-powered drill in there (very short, right-angle type of air drill) a regular cordless drill would never have come close. anyway we drilled then tapped and installed pipe plugs then ground them close to flush with the head surface, bolted the headers back on with new gaskets and haven't had an exhaust leak since (knock on wood).
probably the best way is to remove the heads but i wanted to do it in the car because we had limited time and i had to keep the car on the road to get back and forth to work. it only took us about 2.5 hours to do it in the driveway.
-tim