as said, your better off doing the head as opposed to the exhaust manifold. although by all means do this too!
on something like a cordoba, the manifolds are pretty good from factory, so a port n polished head coupled with a 4-2-1 manifold and stainless would give you a nice gain over factory standard.
problem is, your port and polish wont be as good as a specialists, and you will still need the valves done, head skimmed etc. by the time you price up what it would cost you may as well buy an ABF engine for 150bhp straight out the box.