This is going to be another repeat thread as this is asked so often on these forums. I pressume you are on mfi? if so then I would say full zetec, it will cost slightly more (as only pounds more not hundred and hundreds) but the results will outweigh this. I have just finished building an all steel forged zvh but if I knew when I started what I know now I would of gone full zetec. They are more reliable, easier for parts and drive much better.

The main mod is the valve springs, then all you got to do is choose your inlet, exhaust and management. I small bit of welding/cutting will be required to the front chassis rail but nothing too drastic. Typical prices I think:

Valve springs - £220
Inlet manifold - £300
Exhaust manifold - £350
Management £350 + depending on which you go for
Pistons & rods package £800 (pec forged and h-section)

These are the basics I think and with standard cams you should be looking at an easy 250bhp without breaking a sweat depending on which turbo you use etc

Im not clued up on these at all but there are loads on here who have done this conversion with daft results.