the jackson racing bbk is about 8psi and you can gain a few more psi with an 5.7" od pulley, this will just about max out the blower. as there is no intercooler you will definately need wmi to coll down iats. the focus boys seem to think 200 whp is about the limit from this kit on the zetec.
the jrsc uses its own intake manifold to which the compressor sits on top.
if you take a look on focaljet there are some zetec foci using centrifugal blowers and there is a wealth of information too.