Its all about what you want mate, ive gone all steel zvh, was considering the 16v option but it was just not worth in for what I wanted. The amount of space I would of lost in the engine bay and messing about with inlets and customs part meant it was too expensive. A really good benifit with the zvh is that you basically end up with an engine with the same setup as standard, the engine bay is pretty much stock looking apart from the oil filter location, meaning its no harder to work on. Speak to Simon at sitec racing, he is helping me out a lot with my build, he has been making stupid zvh's for some time now.
Dont get me wrong the above comments are very true, the 16v head is brill and in standard for with standard cams can easily flock 300bhp+, but I fell its a bit over kill for the hastle involved unless you are happy to do that. zvh cheap with great power and torque. 16v quite a bit more expensive, more hastle, lots more power & potential
Chris @ powerconversions is another zvh guru who may be able to offer advise
hope this helps
Home Built/Garric44 Race Fiesta 2.0 (will be ready for 2012) (I hope)