Aluminium block

IMHO- if you need to save the block.
First tig weld the pice back in as closely as possible. Aluminum and coolant (coolant from back then was way more corrosive to aluminum then today’s coolant.) So the tig welder has to adjust for that as aluminum is like a sponge and will have absorbed stuff from the coolant. Look at when you change a aluminum water pump off an old engine that has sat for a while. A lot of junk and part of the pump is corroded heavily.
Once tig welded the machine shop will bore the cylinder for a press in sleeve. Then cut a lip in the top for the sleeve. An undersized piston may be an option. They will freeze the new liner when pressing in to a hot block to allow to press fit. DONOT allow the top hat to be cut from the sleeve. This - when compressed allows the sleeve to stay in place when the head is bolted down. The block will be decked to make sure all is square. Undersized pistons are typically custom made. Not cheap.

The other option is most of above but have a groove cut into the cylinder and a o ring is put in the groove and the cylinder pressed thru that like liners on a diesel tractor engine. Both are a lot of labor and skill.

hope this helps- Syleng1