Copy pasting my post from the thread 4 below yours.
In an sti swap, you will need, engine, custom made exhaust from dp back. Turbo subframe, trans, axles both front and rear, ecu, harness for tranny, harness for engine, rear diff, turbo hood (JDM legacy or USDM Turbo Baja) and a tune. You cannot use your 5speed tranny, clutch, flywheel, diffs or axles.
Is it worth it? It's your car.
What engine? Try and find a usdm V8 sti. They are the most common and easily matched for a full swap.
Bumper/hood? Hood yes, bumper is on you. Hood must be scooped or you can go front mount but that is alot of work and your stock bumper will not fit without alot of cutting.
Q4/5 see top paragraph.
As for showing someone up with a basic car. With a good tune, and full stock engine, you are still only pushing just over 300 horsepower in a car that is generally heavier than the engine is for. If you really want to show people up, you're going to have to put real money into the engine. Subarus in general are not drag cars. If you want to run a quarter and suprise people, for the money and effort, you'd be better off just picking up something rwd and 8 cylinder powered. Now if you just want your LGT to be more peppy over stock, and want some zututu without buying an impreza or a jdm, then go ahead. But don't expect earth shattering 1/4s with just a stock 257/207 in a lgt shell.
Please remember that when you start down this path, you don't get to the other side before atleast 10,000$ US and months of hard work.