When we were looking for a turbo /6 header,we found ONE, in Australia for $1,200.00.Thinking that was too pricey, we built one.... ended up spending $1,000.00 on it and WE did all the work!
My advice? Take a late-model /6, cast iron exhaust manifold and attach a turbo mounting flange to the bottom of it and forget the tubing header. Take the thousand dollars you'll save and buy some really good Wiseco forged pistons and a set of forged K-1 rods. They have matched sets of rods/pistons for this application..065" over.
The late model exhaust manifolds have more strengthening ribs cast into them as insurance against cracking, I am told.