I have done loads of transplants with a zetec but most have been rwd.
st170 Manifold, is that inlet or exhaust ?
Exhaust is good on a Zetec but inlet is a bodge.
My party trick is running them for fek all with the standard ecu. I find them easy but time consuming. Other people just think wiring is witch craft.
So I can not help with the Fiesta. but I can give you pointers with the electrics.
Many people will tell you you are wasting your time and by going Ms, Omex, Dta ect you will half the wiring and get more power.
So it comes down to what you want from the swap. A full race car or a bit more go.
I've been paying around £10~15 for an ecu with the exception of the RS. It needs no mapping and will just pass an mot or even an Iva as long as all the bits needed are used. Most after market ecu's start at £500+ and you will be into it a shed load more by the time its mapped.
Don't waist your money on pre pats ecu's. Latter pats with Obd2 is better.
last project was a rwd st170 with oem electrics.
Budget St170 engine on oem ecu first full run. - YouTube
Current project is a standard 2.0 black top with cheap Rs parts that will stay fwd with the st170 box.
I've done the ecu pin outs and basic pats info for most Zetec's from pre pats to silver and black top as well as the St170 and the Zetec SE.
This is for the silver / black top.
http://www.locostbuilders.co.uk/view...php?tid=179921
This is the Zetec SE
http://www.locostbuilders.co.uk/view...php?tid=199233
This is the St170
http://www.locostbuilders.co.uk/view...php?tid=190440
I will do the Rs when finished.