Even if you could get the radiator from a Focus (and you haven’t told me what year Focus) a radiator designed to cool a small four-cylinder engine probably wouldn’t have the capacity to cool a larger, V6 engine as found in a 2002 Ford Cougar. Perhaps it would work at moderate speeds in cool weather, but a freeway drive in high ambient temperatures would very possibly see it fail to cope. You’d also need to ensure that the radiator suited the transmission fitted (a radiator for a manual car can be different to one for an automatic).

From what I can see, the radiator to suit a 2002 Cougar is, in fact, interchangeable (on some level) with that of a six-cylinder Ford Falcon from 2002 to 2008. Perhaps that would be a better idea, but I’d still be running a tape measure over both cars and taking careful note of where the mounting points are. Or, simply buy the radiator that’s designed to fit the Cougar.

I WOULD buy something else rather than gamble on a Cougar. It was yet another car imported by Ford to fill a hole while it was in an even deeper one with the Falcon. It was a good looker, and I'm guessing that is what got you hooked. It had reasonable performance, though my rating of it at the time was that it was a little too soft. Ford stocks parts and will do for a few years, but will eventually stop stocking them. I would look to something such as a Toyota Celica.