You could make an adapter plate for the T3 as a couple of other Sunbird owners have done. For direct bolt-ons, the later SAAB TD04 will fit as will a lot of the new GT series from Garrett e.g. GT28 etc. Other Mitsu/GReddy/HKS turbos will fit that have the T25 flange (talk to Pontiac Jeff about those).
There were/are different turbo manifolds for the LT3 and its N/A veriants around the world. Here in the UK a company called Turbo Technics produced a very good T3 manifold but these are rare now. Another UK company called Courtenay Turbo also produced one. A couple of companies in Brazil still produce T3 manifolds for the 2.0L. I have one on my engine which comes with an external wastegate.
If your handy with a welder you can easily make your own header as shown here http://www.sdsefi.com/techheader.htm
Stef
Big ass turbo
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