Only a machine shop could really determine the full extent of damage to that head, but from what you posted I wouldn't even bother. It needs to be pressure tested, but more than that is the extensive damage. It cant really be welded, and you cant likely machine it enough to clean it up. Even pressure tested, after that kind of damage it should be fully x-rayed. And you cant pressure test it until the prechambers are out and the valves are pulled. I estimate at least $200 or more in labor just to determine if its leaking or has cracks.

Considering the damage shown it is most likely cracked, and even if its not it will require extensive labor to try and repair it and youll still have a very questionable head.

I would seriously cut my losses and find a good used one. I see over half a dozen on car-part listed under 300TD for $300-400. Thats the direction I would gravitate.

I wouldnt even bother with that block. Back on car-part, they have a whole page of 300TD engines for $500 to $1000. If you can find a decent used motor locally or within reasonable distance you could save a ton of labor and parts and machine shop work.