Why not use oversized valves and have the head machined out to except vauxhall ecotec larger followers this totally opens up the cam choice for you really run an aggressive cam profile , again larger valves = more air especially when your super forcing it into the cylinders he could possibly get the same bhp for alot less boost.
in america there has been a few 1000bhp zetec engines but its a case that they get rebuilt after a few races . I know one bloke i spoke to and he filled all the water jackets with concrete and run it on methernol but it only lasted 2 runs and he was running serious bhp . He changed over to the ecotec engine in the end .
I always look forward to hearing about the zetec as it always gets slating compared to the yb but if its a 700bhp and reliable then surely its on par if not better in terms on not paying the over inflated cosworth tax
26k for a cossie engine compared to 10k for a zetec

cheers paul