as iam very good friends with ian howell ive been watching him do his evo heads , to be fair he has fooked 2 up but its a learning process , he took the first out right out until he went through to the water jackets so he knew whats the limit of material in the actual cylinder head was.now his lastest head looks like it has been cnc machined its that good. zetec heads are very cheap so buy a few and give it a bash if you get better results on your engine then you can give yourself a pat on the back if not you wasted a few quid so its no big deal.
i can post some pics up of my head but remember its a shonky silver top lol
no seriously if you want some pics i will send in a pm

cheers paul