As said they need loads doing,loads of headwork differant cams/pistons, not a cheap option and you dont get much more power than a standard yb in turbo form,you can get them to 260 bhp but they are rare, most ive seen have about 220 to 230bhp
The duratec is very very expensive if you want to be near 300bhp, a standard duratec with tb would not see anyware near 300bhp,so again would need loads of money spent on pistons cams ect ect