I'm not a 1G owner, but are the exhaust ports round?? (from memory I think they are)?
If so, you can acheive a more than satisfactory result buying a piece of 10mm thick flat bar in the appropriate width & length, and use the exhaust manifold gasket to trace the ports & stud/bolt holes. You can then cut each port hole with the correct sized hole saw in a drill press. I used one 2mm smaller than the size I wanted to cut, as they tend to be a little off centre, and so cut slightly bigger.
Maybe I was just lucky, but this turned out excellent on the one I just made for my 4AGZE.