if i were u id keep my 289 heads but just get them ported and polished if u want, maybe resurfaced, its alot easier and u will have plenty of power, i do and didnt even get them ported. the edelbrock manifold u got is good but i would have just gotten a performer dual plane manifold( i love mine).headers would be the first step before u upgrade too much so ur engine can breath better. next i would go for a cam but not too big, mine has like a .448 and .472 lift. as for mufflers, every 5.0 mustang has flowmaster, if u wanna be like everyone else then be my guest. for now i just have some generic turbos from JC whitney and i get plenty of complements but i really dont think it makes much difference as far as power, but what do i know. anyways, get headers they sound great. and a bigger cam. should make a noticeable difference.
