It's a simple unity gain dipole with a balun and UVSJ to combine the dipole with the loop element, nothing fancy. We did it using parts and materials that were mostly off the shelf. We bought the UVSJ of a vendor's shelf and slightly modified the plastic dipole holder from the one used on our V-series antennas.
Here's a "universal" version I made up for other of our UHF antennas.
The actual C2 upgrade kit is a reflector with all this already attached to it. It takes only five minutes to swap out the reflector, move two cables, and snap the rods into place.
Tech data sheet is for the C2v is available under "Documents" on the product page for the ClearStream 2 Complete which includes a C2v.