I am about to install my aftermarket stock hybrid turbo.  The turbo cost $800 from the RX-7 store.  More expensive than other turbos, but considering it will be bolt on it it is worth it.  Here are the pictures.  Note that the hybrid compressor is even larger than the TO4, and really puts the stock compressor to shame.  They also did a good job with porting the wastegate, and the turbine wheel looks way more open than the stock.  there is no doubt that I will not be overspeeding this thing, so if it fails heat is the big problem.

 

Dave Leonard