Honestly, not much. You can't put an exhaust on since it will be swaped, or changed when you pop on the turbo, you can't do a chip, or injectors, or internals, or anything really to the engine.
Intake, and maybe some better ignition stuff.
Literally when you install a turbo ( even a kit turbo) you have to change everything out of the engine ( pistons, injectors, exhaust manifold, timing, vavles, studded heads, engine control modual, oil feeds, cam, etc) to take full advantage of the power of the turbo. Not to mention the hours of tuning, and dyno time to get it just right.
You could to some transmission work ( shift kit, gears, short throw shifter, new clutch), Limited slip differential, coil over suspention kit, new CV shafts, brake kit, etc.
Honestly doing anymore engine work then intake and electrical on a car that is going to get a turbo is useless.
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