you did well by taking it to a machine shop... The guy at the machine shop
has handled thousands of heads so I would not dismiss his advise so readaly.

It is true there are folks that weld heads with good results. They preasure test afterwards and normally you would use some one with years of experience. I would seriously consider this option.

The actually instructions on turbos say to exspect cracks and go ahead and resuese if the crack is not in a certian area or past a certian length.

There is a new thing out called alumaoloy. It looks like a welding rod but it melts with a torch and its used with cast metal....

What I think I would do is this: I would drill each end of the crack to stop it from expanding. Then I would enlarge the crack. Then I would use a torch and fill it with this alumaoloy. I would sand it flat and put it on and see if it holds preasure. Your risk is a new head gasket and redoing the work...

good luck