Well, I'll get pix soon. No, these are not like GR-874 connectors at all. They are large (1.5 - 2.5" diameter, with convoluted ceramic inserts, and threaded clamping rings. They look like thay are made for very large voltages at frequencies below 50 MHz, maybe. There are 4 adaptors in one of the end covers, and a coax extender in the other. Some of the connector part numbers are : CBRS UG-34/U S276-1306P1 CBIB UG180A/U CBRS UG-222/U
The whole thing is in a cylindrical can 12" diam x 20" long, with removable caps on each end. the caps have really big O rings to hermetically seal the thing, which is why a 45-year old power cord looks like new. (The power cord is to run the cooling blower.)
Jon