Good project always liked the idea of a RS turbo van.
This is a straight forward conversion as it will all bolt straight in the only part that may be a bit of a headache is the wiring but there is a company called the RS Centre that sell a RS Turbo conversion loom if you dont fancy doing the wiring yourself, i have never used one but sounds like it might make the jod easier.
I mate of mine did have a complete but rusty S2 for sale a couple of weeks ago that is running around 170bhp that wasnt alot of money could find out more if your interested.