The BP heads ARE interchangeable. The manifolds will both bolt to the 94-97 Miata head and vice versa. However, the alignment of the manifolds in the cars will not work without modification. For example, a Protege manifold installed in a Miata will have the throttle body pointed at the firewall, whereas a Protege with a Miata manifold will have the TB pointed toward teh passenger side of the car.