ok where to begin...
you can't bore your ze to 2.8L..the maximum you can go is 2.7¸..upgrading the internals of the engine is almost useless if you dont go turbo..p&p the intake manifold is a great idea and is done by many owners..shaving the heads can give you a little hp but you can't shave too much cuz you'll mess with the timing and clearence with the valves is an issues too on our car..they don't do performance oil pans sorry...stiffer valve spring is good if you want to rev the engine higher but you should'nt cuz we start to loose power after 7000rpm so it's useless..i really doubt you can go up to 350hp...well it was never done on a N/A set-up..anyways i hope you have big$$$$$ because with all you jsut said you won't go under 15000$ for sure