[teh DIRT]

you came to the right place.

Heres the deal. The ej20 into GC (93-01 Impreza) is a bolt in job as far as mechanics. You will need either a jdm WRX (GC) crossmember or a USDM turbo-legacy crossmember. This is to accomodate the turbo headers.
As for the transmission, and EJ series engines transmission will bolt up to any other EJ series engine. For auto to manual you will need a few things. Including-Clutch master cylinder, MT flywheel, MT Starter, MT pedal box, MT Transmission Control Unit (TCU), MT driveshaft, MT differential. I think thats about it. This would be a great time to look for a junkyard with these parts. If you need help, ask me....i know of atleast 2 junkyards that have GC manual imprezas.
Now that the engine and transmission are taken care of, lets move onto the wiring. You will need an ej20 ecu along with all the harnesses. Then you will need to mate the harnesses together to make them work. This is where my knowledge ends, it is a very long (more than 20hrs of work) process that take a lot of knowledge about this swap.
Your best bet is to do everything that you can as far as the mechanics. Get the engine and transmission in and secure. Then take it to a shop that knows a lot about this swap. There are a few in the tri-state area that have done these before and would gladly help you with all of the wiring for a price (close to 1k).

Hope i helped.

-pete