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Apparently, Series 5 RX7 turbos have a 0.88 compressor cover and a 1.0 A/R exhaust housing. They are both oil lubricated and water cooled.

This is a close up of my altered exhaust manifold.

This is what the whole thing looks like. It was surprisingly easy to weld the mild steel to cast iron, I just used stainless electrodes in a stick welder (MMAW  for the picky people out there). The manifold saw a few weeks of heat cycling and has developed no obvious sign of cracking so I guess that she'll be up to the task for quite a while.

this is a picture of an RX7 turbo next to a T04. The compressor size difference is fairly obvious....