i'm thinking of upgrading the suspension on MY97 UK Turbo for road and very occasional track use but i'm a bit confused....

Are all the Koni 'sport' top adjustable struts inserts which require modifying the exisitng struts?

I'd prefer just to replace the old struts with a completely new unit and use my existing Eibach springs.

Would really like completely new unit, damping adjustment, use my existing springs and all for under £600!

Is this even possible? Any advice please.....

You're correct re the Konis.
Try a search for KYB AGX.

thanks mate, i'll give it a try