Hi,
yes, the ELA M 260 was made by AKG. It is based on the Telefunken AC701 tube. The capsule is basically the same as the AKG CK28 which was used with the C28 and the C60 =>
AKG's CK26 & CK28 capsules
The powersupply is the same as with the ELA M 250/251, the M 950.
I speculate that the ELA M 260 is closely related to the C60, (maybe even more so than the ELA M 251E is related to the C12.) But while the C60´s output transformer is located in the PSU, the transformer of the ELA M 260 has to be in the mic body as it uses the M 950 PSU.
With a housing diameter of only approx. 17,5 mm it´s even a bit slimmer than a C451.
Telefunken USA offers a model that confusingly is also called ELA M 260, but it seems to have not too much in common with the real one. According to their website, they use a different tube (EF732) and different capsules (original AKG capsules don´t fit), and most likely a different transformer = different mic.
Attached are pictures of an original ELA M 260. (sorry for the bad image quality)