Never say never, I guess, but with the SM sharing the Ds almost unique mid-engined front wheel drive configuration, and space under that beautiful bonnet already exceptionally crowded, I'm none too sure you'd get a Chevrolet to fit. The SM engine as I mentioned is incredibly compact and, Citroën being Citroën, they were determined to fill every spare inch they could with anything they could fit in. Still, I could be wrong.The SM looks great however the V6 engine is a big pain in terms of reliability.
Blown head gaskets are frequent and the accessibility to the engine components is difficult. If I had one I would definitly modify it with a different engine like a modern small block Chevy if it can be installed with the front transmission. I'm sure that can easily be done in the UK !
Regards,
Brett