In have done a S2 zetec conversion for a customer last year.
He sourced most of the parts and our job was to get them fit together.
I try to recall from memory, so i probably forget some things, if you need details just ask.
Engine is a 2L black top zetec,
Intake 45 FAJS Weber copies, the manifold should be available.
Exhaust a stainless turbo manifold from UK.
I cut the flange from the manifold, and welded the exhaust piping, sadly i cant remember which muffler he sourced, it is an absorber design but the car is not annoyingly loud, and it was small enough to fit it under the luggage box.
Motor mounts are custom, i installed the engine as far to the front as possible and used the rule of thumb, if your thumb fits between engine and frame the is enough space. ( I have skinny thumbs)
Gearbox mount is custom also.
Alternator came from a komatsu lawnmover, i 3D printed all brackets to testfit and had them lasercut later, from the same design.
Transmission:
NG9 with twincam bellhousing.
The bellhousing was already modified with an intake bearing.
the NG9 do not have the possibility to take load from the rear driveshafts, so i had to use the 336 differential internals in the NG9 box.
Remember that i had to shorten the spring in the gearbox end to make shifting gears easier.
Customer designed a cable shifter setup.
Clutch:
Zetec clutch with a Renault R21 disc.
I had to turn an extension for the throwout bearing, still have the design in cad if someone is interested.
Starter:
One of the biggest problems, Renault one worked but sounded horrifying, zetec did not fit the bellhousing, did an ugly hacksaw mod to get it working temporarily.
Next try will be an twincam with a spacer plate, but not installed yet.
Ignition is a NODIZ
https://motorsport-electronics.co.uk/products/ignition-only-systems/nodiz-pro/Customer sourced , but this thing just works, sensors are zetec stock, ignition coil is zetec stock.
But beware the rev counter does not work.
Cooling tubes are S2 europa
Problems i recall.
The driveshafts are at an extreme angle as the differential is far more behind, so far it seems to be no problem but there is no long time experience.
Lower links have to be custom made, or shortened a lot, due to the driveshaft angle.
If pictures are needed i can get them within a week or so.
Regards