The puzzle's photo is indeed only captioned as a Coupé online, and there's no trace of it in my reference books.
The Saturn is somewhat bigger so I guess it isn't one. I don't really know how to tell apart a C90 from a Comet. To add some confusion some cars are even described as "Comet C90".
I'm reliably informed by a fellow AutoPuzzler that this is, as I originally thought but couldn't find any proof of, a Comet Coupé, so we'll declare it solved and move it.
Well done.
One of the reasons I doubted the identity though is that I had the following picture which was captioned as a Comet Coupé, and it is quite different in detail, e.g. the side windows and the slope of the rear.