Why start with an expensive st170 engine when you're foing to have to get loads of headwork done, new pistons/rods etc, you may as well just start with a boggo silvertop

by the time youve got a peaky nasty to drive 250bhp out of one of those you may as well have bought a duratec and got the same power cheaper, because the zetec will bankrupt you for that power, and you wont get it right with the first attempt anyway in my experience

If you insist on the zetec, or the duratec for that matter then have a trawl of the kit car/caterham/westy forums as they all have better info than on here

I'm not sure you realise the cost of that power target?