it can be welded...
you'll probably have to pull the engine out and tear it down first though...
tig welding and oily surfaces do NOT mix.
I had my custom cylinder head for my volvo/ford hybrid done at:
www.eagleautomotivemachine.com
they arent local to you but here in atlanta (big ass city duh) they were the only machine shop that would weld aluminum like I wanted, and they did an AWESOME job of it...
how the hell did you crack the block by those threads anyway? I'd love to see a picture of this.