All cosworths had a 4 cylinder 16v engine be it 2.3 or 2.5. Only the 2.3 was imported to the USA and Canada. If you find a 2.5 its a grey market car. There is no such thing as a Cosworth 2.6. Thats a completely different 6 cylinder engine. I really doubt the 2.6 car you found is a genuine cosworth because the 4cyl and 6cyl cars had completely different radiator support which has to be welded in. The Cosworth also had self leveling rear suspension. Check the vin number. That should tell you exactly what you're looking at.
Cosworth engine looks like this.
