Chasing vacuum leak - found torn thread on carb stud - helicoil repair

[EIRE V8]

I've been hunting for a vacuum leak, and while I'm not sure its the cause, I've found that one of the corner carb studs has torn the threads in the stock intake manifold.
I was going to use a Helicoil to repair it, but anyone know what size I should use so I can re-use the stock hold down studs?

[metallicareload99]

What thread is the surviving hardware? Been a long time since I had a stock intake, but I'm guessing you need a 5/16" coarse Heli-coil kit