I tried this method when I had my intake and exhaust manifolds surfaced as a unit to remove the warp. I was not pleased with the results and went to the process I described above, which has worked flawlessly. I also think eliminating stepped washers makes the assembly much easier especially...
It is a very easy process to tig weld the seats and recut them to the same step thickness as the header. You can also use this process to cut different heights for the intake seat to match the seat height for a factory exhaust manifold that has been surface to remove the warp (each seat height...