Complex sentence: The RB-66C was a specialized electronic reconnaissance and ECM aircraft with a crew of seven; 36 of these aircraft were built with the additional crewmembers housed in what was the camera/bomb bay of other variants.
Split into simpler sentences: The RB-66C was a specialized electronic reconnaissance and ECM aircraft with a crew of seven; 36 were built. The additional crewmembers occupied what was the camera/bomb bay of other variants.