You can do what some call cold welding, some call pinning.
Hard to describe, I will do my best:
You have to get some cast iron pipe plugs/ or bolts.
The size depends on the hole you are repairing.
Drill the bolt hole out so you can tap it and install the pipe plug, some people use tape on the threads, then cut the plug/bolt off almost even with the head casting.
Drill your next hole so that half of the hole will be on the plug you installed and the other half will end up on the cracked area, run the tap threw it, thread in next plug, and cut remainder off almost flush.
drill next hole half on your 2nd pipe plug, and half on crack.
You repeat this until the crack is 100% gone, in both directions.
Then grind repaired area 100% flush, install your manifold or header, or use the gasket, to locate where to drill the final hole, that you will tap in correct size of manifold bolt. that broke in first place.
I know it takes a lot of time but its not hard work, and I have seen it done to combustion chamber of cylinder heads and no issues.
here is a site with instructions, once there go down to pinning :
https://www.enginebuildermag.com/2012/01/cylinder-head-repair-methods/