I concur with mrfix. I have done so many I'm getting a headache thinking about it. I also would weld a nut to the existing stud even if it broke flush with the head, just straight down the center with the Mig welder. The heat from the welder will also loosen the broken stud. If you choose to drill, just measure the depth of a hole and mark the bit with tape so you do not drill too deep. Ford now makes a stainless steel stud and nut.
Ford replacement Stainless steel Stud part number, W703902-S403
Ford replacement Stainless steel Nut part number, W701706-S2
- Torque the studs in the cylinder head to 71-115 lb-in (8-13 N-m).
- Torque nuts on studs to 204-239 lb-in (23-27 N-m).