There was a handful of detail changes between the Interceptor Mk II and the SP, including the louvred bonnet, slightly different lights treatment and the addition of a vinyl roof on the SP.
Most of these changes were carried over to the Mk III Interceptor, apart from the vinyl roof and the fact that the louvred bonnet had far fewer louvres (and it was only an option).
Your puzzle car seems to be a Mk III with an SP bonnet..!