[mas]

I meanwhile was able to get hold of some additional infos about this mic.

My initial speculation that the ELA M 260 is related to the C60 was wrong...
I contacted AKG´s service department and was told that the amp of this mic (called ELA M965 BTW) has little to do with the C60. Instead this amp is quite closely related to the circuit of the ELA M 251/250.
Obviously AKG had an quite economic approach regarding it´s mic circuits (the amp of the C28A is very similar to the ELA M 251E´s - even more so than the C12´s).
However, the transformer used is not the T14/1 (like in the 251, C28, C12, C24) but another type called "T199/1". It is slightly bigger than the T14/1 and fits snugly inside the mic, filling the full inner diameter of the slim housing. It offers 200Ohm or 50Ohm output impedance.

Also the capsule mount is slightly different than the usual AKG CMS mount, the difference being that the contact pin is located on the mic body instead of the capsule. That means that the AKG CK28 as well as CK1 (CMS system) and all the aftermarket capsules cannot be used with the ELA M 260. Other than that the M260 capsule is identical to the CK28, including the thread.
As the micbody (ELA M965) is used with either the M260 or the M261 capsules, it has an additional contact (pin) that is needed for the M261 capsule (switchable pattern – omni, cardioid, fig. eight). On the capsule side of the extension tube it´s not a pin but a wire bail. (see 1st image)

The second pic was on TelefunkenUSA´s website while their new mic was under development (downloaded 2003) and shows an original 260 with new PSU and cable.

The third pic (crop) is currently on TeleUSA´s website and shows an original 260 from another perspective (in the booth on AES oct.2006).
It too shows that the contact pin is on the other side, not on the capsule.

So it appears that the ELA M 260 is the least versatile of the AKG-made SDC modular tube mics because only two capsules fit (with the multipattern M261 being extremely rare).
But as the C28 isn´t too far off designwise (approx. like 251 vs. 251E), it´s a more easily available and more versatile (capsule-wise) alternative.

I didn´t find a brochure or specifications yet.

Unfortunately I don´t have better/more detailed pics by now. But as Telefunken USA seems to own (or at least have access to) an original 260, maybe they could post some better pics. Would be great.