A good (GOOD) welder should be able to TIG the head, using a high nickel content rod.
Most important aspect of the job is to properly (slowly) preheat the casting, repair it fairly quickly, and then post heat, to gradually cool it.
Using an oven with ramp/soak controls is a plus, but an operator can turn the dials too.
Ideally, they'll have a data recorder attached (via thermocpouple) to log the rise in temp over time, the repair, and post heat-cooling process.
Let me guess, cracked between cylinders 2 & 3 exhaust seats?