but a thread up in the rs turbo section about your engine plans and you might get a better answer, but here goes my limited knowledge one....

for that sort of power reliably youll want forged pistons and rods

a 2wd cosworth T3 turbo (they can flow more power than an RST one) - maybe look at getting it rebuilt with roller bearings if lag is a concern of yours

some cams will be needed, failry mild ones but a bit more aggresive then standard

head work will be needed, and bigger valves may be required

yuoll want a bigger intercooler

deffinatly need it to be EFI - i think yuoll need a differnt throttle body (cosworth one rather than fiesta one would be preffered) and different managment (aftermarket again would be best but cosworth L6 - from a 2wd or L8 form a saph 4wd or P8 from an early escort could control it, but not the one used from a later escort

air injectors may be needed for a bit more control

the gearbox will need uprating - there a quite a few 'kits' out there thatll be able to sort this out, and the diff will want either re-jellying or a new diff put in its place

i may have missed a few things, i only have limited knowledge, but that should give a really reliable engine