Suspension and brakes: You could start with KYB AGX struts, Sprint or Intrax springs, Speedbuilt sway bars and strut braces. Then you could swap your front brakes to Corvette calipers and Camaro drilled and/or slotted rotors, Goodrich stainless brake lines, new brake fluid, get some drilled and/or slotted rotors for the rear and some Hawk or EBC brake pads at all 4 corners.
For your engine, there's all kinds of things you can do. Look for anything for a Cavalier or Sunfire 2.4 engine, it's the same one as in the Alero and will all work the same.
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