I have a tuning book on zetec motors and they claim almost 400bhp from a stock engine....except cams and ARP rod bolts.
As for exh manifold, you can use the std focus one, or buy Spa cast exh manifold , with the intake you could make one up as there's not much for rwd ....however there is a Rover 220turbo intake that can be fitted by making an adapter plate(big in UK) , I have one I'm going to use on my zetec . valve springs can be sourced from Peugeot 1.9 GTi from memory, or simply fit washers to up the lb rate.
PM me if you need more info...ecu, clutch etc