Questions come up occasionally regarding the K-77. It is a rebranded EV T-35 which passed strict Klipsch QC. According to an article, PWK selected the EV after EV adopted the Avedon phase plug. It was first used in a K-Horn in October 1959. University eventually acquired EV and published a spec sheet which is more elaborate than what EV published. My read is that horizontal coverage is greater when the unit is oriented with the long axis vertical -- i.e. that the patterns shown were obtained with the unit oriented as shown in the picture.
Per the timeline for K-Horns: The first three-way Klipschorn incorporated a Jensen RP203 tweeter. This tweeter came from the famous Jensen G-610 Triaxial 15" driver and required considerable negotiations with Jensen. It was not until mid-1952 that all Klipschorns were three-way. A two-way Klipschorn with response to 12Khz was generally adequate for program material up to that time. The University MID-T- 4401 replaced the Jensen unit as the tweeter of choice later in 1951.
WMcD
T35A University Spec Sheet.pdf
T35A EV Spec Sheet.pdf
Avedon Design Patent on T35.pdf
Early T35.pdf
EV Avedon T35.pdf