What does posting a thread regarding a very expensive, high budget and very high spec ZVH with specific pistons and management, along with purpose built inlet manifold, this is without mentioning the 6 speed gearbox offer to someone looking for 250BHP other than suggest if you have money to burn this is fun way to do it

I dare say you would not get much change from 4.5k (probably more) to get that engine to get it your car and mapped. Most peoples cars are not worth that much

The fact that Simon was running a 16v head which has been replaced by the 8v head puts him in a position to comment on the differences and with the same engine spec he stated "It feels about 75bhp down with all the rest of the engine, turbo and install been the same".
This simply suggests that the Zetec is a better head and cam setup as such to remove it and replace it with an item that is less capable seems a poor choice - Its ok if you are a business like Simon who has sold the 16v head to a customer and only went to ZVH because he had a spare 8v head..
Information such as this does not seem to suggest the ZVH is the better choice imho