As BDA stated, the Zetec is a relatively simple swap for a Twin Cam car, the 4AGE is a well documented swap for the Renault powered cars. John Pels makes a "kit" to convert the Europa to the 4AGE. You can swap a Zetec into the S2 but it does require sourcing a Twin Cam bellhousing (modified to clear the water outlet at the back of the head.
Some little things that I've stumbled across in converting to a Zetec are as follows:
Clutch disc has to be either custom made or you need to source a 1.6L or 1.8L Zetec flywheel (which never came to North America)
If you swap the flywheel for the smaller one you need a clutch cover to suit
Mounting the starter requires some modifications
Motor mounts have to custom made (though my whole build is custom)
The oil filter needs to be relocated
The "blacktop" waterpump needs the hose connection modified to clear the chassis (or at least mine did)
The stock alternator setup doesn't really work in the Europa, so a smaller relocated one is a must (but the waterpump must still spin opposite to the crank for the "blacktop", the silvertop (early) waterpump can be modified)
Induction system is up to the builder, along with the exhaust
The ignition system is very easy to convert to Megajolt (and/or Megasquirt)
As for the 4AGE, the Pels kit is fairly complete, and Dave L on the yahoo group has made up a bunch of motor mounts and shift linkage bits to aid in the install.
Beyond these two motors, rotaries have been swapped, along with the Duratec (or MZR motor) but these require custom adapters to mate them to the Renault gearboxes.
