The YRF-84K, redesignated from the modified YF-96A. Used for initial FIgher CONveyer (FICON) testing with GRB-36D. The YF-96A aka "first" YF-84F was modified by addition of a fixed hook mounted on the nose which enabled the aircraft to engage the capture trapeze deployed from the bomb bay of the GRB-36D mothership. Also, the nose probe was removed from the nose intake splitter, the V-shaped windscreen was replaced by the production flat-style windscreen, bracing tapes were added to the canopy, and G-model style auxilliary intakes were added. See YF-96A and YRF-84K comparison photos.
Subsequent to testing with the YRF-84K, FICON purportedly became operational for a short time with 25 RF-84K aircraft based at Larson AFB, and the GRB-36D aircraft operating out of Fairchild AFB, both bases adjacent to each other at Spokane, Washington, with RF-84K aircraft.
The YRF-84K is on permanent display at the Air Force Museum, Dayton, Ohio.
YRF-84F 49-2430, formerly the YF-96A aka "first" YF-84F, attached to the trapeze under the GRB-36D during FICON tests. This photo was apparently a widely distributed publicity shot, as it has appeared in many publications. I obtained this photo about 1956.
Links to photos at other sites
Air and Space FICON Page 1
Air and Space FICON Page 2