>The stock turbine housing is just plain too small for aircraft use.  
I'm not entirely sure that's true. Perhaps not totally ideal, but it can work, and it's a lot easier / cheaper to install.  I'm now running the stock '89 turbo modified to look like a T04-V1 (I think) by http://www.turbonetics.com.au/ and balanced to 120k rpm.
It seems to be behaving quite well so far. 48MAP at Sea level = enough of power to turn my big 84 pitch prop at 4070. 46MAP at 10,000' - no problem - prop rpm 6100 and 235 kts TAS.
John

Well John, you are the one flying a turbo rotary and I still fly behind pistons. so you must be right! Nothing like real world experience. If I recall you fly a Cozy? How many hours do you have on the turbo now John?