The ring gear is fine, main shaft does not locate in the crank spigot bearing. ( I would love to know why the st has a spigot bearing and a Zetec does not ? ) I haven't measured it yet but you will need to space the thrust bearing more than 5mm. The Vauxhall clutch plate is 228mm and the Zetec 1.8 fly' is 220mm so you will want the 2.0 fly', 240mm