SPO-1 was a typo writing fast.
You´re right foxbat, it seems that no P variant got an RWR, only S and late PMs, in wich was installed under the navigation light in a smaller antenna.
But, if the system is simple to incorporate in real life I don´t see why a P can´t have it. You would be suprised as to how many modifications and incorporations aircraft receive in the field. I will think what to do.