The more reliable sources of information I've been able to dig up regarding the strength of the drivetrain seem to be well summarized in the following quote. The knowledgable folks from I-Speed that have much experience with these swaps also mirror these statements.
The structure and strength of the transmission is realtively unchanged since the 1993 Imprezas (not necessarily a good thing). There are some exceptions though: the turbo Legacies had a more uniform metal composition in the gears while the new STi comes with a robust 6-speed. Other than that, the gear strength is almost the same.
That being the case I would rather not shell out thousands of dollars for something that's basicly not going to do much good in the end and just end up being alot more labor and hassle. If it breaks I'll attempt to address the issue at that time.
The general ideal of the stage one of the project:
1) really used 5MT AWD 93-95 Impreza L (<$1,000)
2) used EJ20 w/ ECU/harness and crossmember. (~$1,000)
3) used TD04/Intercooler. ($?)
5) used HKS downpipe/uppipe + ghetto ass catback ($?)
6) possibly an used Subaru OEM wheel/brake upgrade (WRX/RS?).
Am I missing anything important?
I've got the STi and I plan on keeping it for a few years so I'm not looking for the ultimate street car with this car but hoping for more of a learning experience and something I won't mind thrashing. I'm not even sure I'll be registering the vehicle for street use.