I have no inside information, but it looks very much like a derivative of the 657cc, 3 cyl, fitted to the Suzuki Cappucino sports car.
The engine is an absolute cracker, beautifully made and makes a lovely sound. The quality of machining and finishing was more akin to a bike engine (i.e lovely); though the engine was designed for, and started life in, Japanese home market "K cars"
I am slightly confused as to why Caterham are going this route though, as the Sigma engine in the current entry level cars suits the Seven beautifully.
Bud