As others in this thread have said, it is better to start out with a FWD 3800 (Series 1, 2, or 3 - your choice) if you are doing this conversion in a Fiero. All of these engines will directly bolt up to a transverse type transmission (manual or automatic of your choice) which means no bellhousing adapter plate is required - as one would be if you tried using the RWD 3.8 block with one of these transmissions.
If you want to go turbo, I recommend you start out with using a Series 2 or 3 engine that came from the factory with a supercharger. It'll come with the stronger connecting rods, pistons, and pins (than what N/A versions of these engines got). It'll also have the lower compression ratio (8.5:1) vs. the N/A's 9.4:1 which will allow you to run more boost and help keep detonation under control if using pump gasoline. I would stay away from Series 1 and older FWD 3800/3.8L engines simply because of lack of aftermarket support concerning performance parts.
What I recommend you do is remove the supercharger and install an N/A intake. My recommendations are either the all-aluminum L26 Series 3 N/A intake or the 95-02 F-body 3800 intake. The 95-98 F-body intake would probably be the better choice since it came with a cable-op throttle body unlike the later 99-02 F-body intakes. The L26 intakes only came with DBW throttle bodies, but you can buy adapter plates to convert over to using a cable-op throttle body easily and cheaply enough.
Using an N/A intake on an engine with SC heads gives you 2 sets of injector holes since the SC heads have injector holes machined right in them (N/A engines have the same heads, but the injector holes were not machined in them). You will either need to plug 1 set of injector holes or switch over to N/A heads. I am running a set of ported Series 2 N/A heads on my SC Series 2 block in my Fiero using a turbo.
As far as twin charging is concerned (ie: running a supercharger and a turbo), I would recommend against it. The supercharger is going to end up acting as a restriction once the turbo's boost comes up and all it is going to do at that point is just heat up the incoming air more. Ditch the blower and run a good turbo and intercooler and you'll never have a want for the supercharger. Modern turbocharger technology has advanced so much in the past few years the issues of "turbo lag" are pretty much a thing of the past - as long as you are willing to spend the money on a quality, name-brand turbo and not something made in China, South America, etc.
Having said that, I've done some pretty incredible things with an 80's technology turbo (from an 87 GN) on my 3800 Series 2. So you don't need to spend a lot of money to end up with a pretty fast Fiero if you go the 3800 Turbo route.
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[This message has been edited by Darth Fiero (edited 10-21-2013).]