I used one of these for nearly 20 years, can't remember where I bought it now. It is stamped with the California Amplifier tag but I think ADL made them. There were at least three versions, rp/1, 2 and 3. Because the scaler is fixed these feeds need extension bolts to get them to the proper focal distance for the particular dish they are used on. Once they are set properly, they are a very good feed. Did a search and found one here, I guess mine is the RP-1 California Amplifier ADL-RP1 : C/KU Feedhorn | CZECH AND SLOVAK DX SATELLITE CLUB
Looks like a RP1 C/KU By National ADL. I have the RP1 C on my dish since 1989. This feed is better than the Chaparral and other choke plate feeds. It uses dual hybrid moding champers to take the out of phase energy and put it back in phase. It then sends it to the feedhorn throat.