Are you sure it is cast stainless? We have done the exact same thing to three sets that were of the 1985 or so vintage and they were made from welded stainless tube....you coud still see the seam on the tubes. These exhaust manifolds are a cheap way to get block hugger headers.....they sell on EBay for sometimes $30 a set. You take the ugly sheetmetal covers off.

One note, of the six manifolds that we welded using MIG, one warped slightly and we had to tweak it back. If we had thought of it, we would have bolted it to a junk head while welding.

mike in tucson