Evidently the European Telecommunication Standard REN is defined (REN 1) as a simulated ringer detector circuit consisting of a 55 H inductor in sries with a 7 kilohm resistor, and is based on the characteristics of the dynamic impedance of a type 59D bell movement.
From my extrapolation method described earlier I reckon the 59D (the one with the 4000 Ohm @ d.c. bell-movement) is 7186 + j8275, or a Z of 10960 Ohms at 25Hz, which near as dammit fits the spec.