Sunn listed the JBL's in their 2000S cabinets as JBL D140F speakers, though the D 140F-6 indicates a 16 ohm inpedance. I suspect that since Sunn showed their 2000S amps with 2 2-15 bottoms, that they may, very well, have used 16 ohm versions of the D 140F. This would let users use 2 cabinets, each showing the amp 8 ohms, and only showing the amp 4 ohms when driving 2 cabinets. Since these amps did not have impedance selectors, they switched from 8 ohms with one cabinet connected to 4 ohms when a second cabinet was added.
The Sunn guitar versions (1000S, and 1500S) used the JBL 15S, which was very sinmilar to the JBL D 130F speaker.
Tom