It takes some people decades to become good welders, and I assume that "cold welding" is not common so it's something a good welder would take time to learn.
You will also have to have a machine shop re-deck the block when you are done, so start adding up costs and make your choice.

 

^^^
+ 1

 

First why not try see if it seals ?? You have nothing to lose but gaskets and time

If you attempt to weld this the block needs to be machined back to a flat a level surface $$$

***Explain this Cold welding I might know it under another name??

Any filler metal has to match as close as possible the base metal so the thermal cycling matches ( Which means it expands and contracts at the same rate or very close)

Most Cast Steel and Cast Iron needs a pre and Post heat