If you are going to do the job correctly the welding is the least of your problems.
The guy that will re-drill and tap that hole will know a tig welder.
Actually anyone that is equipped to drill and tap that hole probably has a tig welder.
if welding is the least of the problems - what are the major problems?
My guess would be either be getting that hole in the proper position/angle or why it cracked in the first place/do you need to get the whole head crack tested before proceeding.
I just want the crack reinforced a bit, at least at the top, so it doesnt get bigger when a new injector is installed. Theres plenty of thread down in the cylinder head body so this is for insurance. The injector seals against teh base with a special 'washer', not against threads. A bead of aluminum on top of the existing crack type thing. I understand that getting it clean is the challenge.
Pressure testing might be a good idea but I dont have pressure testing money and hunting for 1.6TD heads at the yard used to be a thing but they dont just dont come up very often anymore.
These heads need to be lapped prior to installation regae time or money.rdless..a popular method thats been used is fine sandpaper bonded to glass or a mirror.