Welded combustion chambers?

Last time I was in Dan Dvorak's shop he was attempting to what looked like braze brass or something similar on the open chambers of junk big block heads.

As I understand welding cast iron: nickel rods, extreme preheat (glowing red hot) your iron piece, & after the welding is complete, it must be cooled down in stages, kinda like divers in decompression.

People do this for rare hemi, etc. matching numbers components.