will a 08/09 aluminum valve cover fit my 02 motor? If it does are the bolt holes and gasket the same?

NO, 02 - 05 are plastic, 06 - 09 are aluminum. they do not interchange.

Only if you change the head - GM revised the head/VVT design in 2006. The late model head is good for 15 HP in stock form over the early head.

Port the head and pick up 40HP.