Ouch. You might wanna consider having a machinist heli coil it. There's very little room for error in the plane of those particular threads, as they position the needle end. Then there's the softness of cast aluminum factor. If it comes to that, you might supply to the machinist or tool maker the heli coil(s), tap and drill, to save some money and time. It may not be a size they see every day, and their time is your money. I believe the taps for heli coils are a non-standard size.
