Roko,

join this site

http://forum.fordsierraclub.co.uk/

and copy and paste your first post here on there

There are some interesting DOHC conversions on that place, I have a n/a 16v engine ready for my Sierra, a bunch of people done this in different ways and one or two 2.3 8v conversions, that when you open the bonnet look exactly standard like your current 8v - that would suit your "Statens Vegvesen".

Join the site - it's sometimes slow but you will get the answers you are looking for