I'm glad somebody asked this as im looking at turboing an st 170 engine for my mk4 escort build!
Mmmm.the only question is over the vvti..to run or not to run??
Lose the ST head all together, again after speaking with Simon @ Sitech he advised against using them as they warp at the first sign of heat making them unreliable when turbo'd.
Fit a black top head, 1.8mm FRS Head Gasket FINIS 1361410, ARP rod bolts and your good for 350bhp with the correct turbo etc.