'ello mate

I believe that the later zetec engines did have the starter motor positioned on the back of the engine, so might be worth using a gearbox from a later zetec engined motor. You should eb able to get the gearbox from a zetec engine into the Mk4 engine bay with a few little mods.

Not sure when they changed and started putting them at the back of the engine but it is done so might be worth finding out.

Soz cant be of anymore help but might help you to know that it can be done