The modifications to this variant were:
(1) double extention possible of 40 inches of the nose gear for catapult launch. It could be extended before aircraft launch from the smaller UK carriers like the HMS Ark Royal and HMS Eagle enabling a far better take-off launch performance. 
(2) twin reheating Rolls Royce Spey engines with a different thick bulged aft lower fuselage shape and different exhaust/afterburner. Air intake door aft of main gear doors.
(3) wider air intakes for the required air flow.
(4) modified cockpit with a different layout of instruments and it also has a small flying stick for the back seater navigator/ co-pilot. Also a Stick Positioning Device was fitted to enable setting the required tail plane angle. 
(5) slotted stabilizers

So this variant was quite different than American manufactured Phantoms!

For more information, check out the references suggested and look at the British F-4 page here on this site....

All the kits have very fine recessed panel lines and good decals. Cockpit detailling is fine with raised details and nice seats. Only some minor additions of sprue and tiny bits are required to get an excellent cockpit representation.

The Fujimi kit #H-8 "Yellow Bird" represents a F-4K of the FAA / Royal Navy. It is the primary kit used here in this building report. (It is noted however that also some other Fujimi kits were available such the F-4 from Alcock and Brown and the F-4M kit for the RAF).

F-4K
The F-4K kit needs minor filling only. I used some putty at the intakes and the lower joint of the forward wing and the forward fuselage. Stores are fine and the details like the gears need carefull detachment from their sprues to prevent damage.

 
Otherwise it can be assembled straight out of the box.
For the cockpit area, nice etched metal details are also provided in this kit.

Cockpit detail is fine, seats required only some smaller added details. Also, I got an NeoMega set for some Martin baker seats used in many FAA and RAF aircraft. These will be used on the FAA aircraft models made, such as Phantoms.  Cockpit of the F-4K has Martin Baker mk. H5 seats, these were later updated to H7 standard (as on the USN F-4J). 

Overall colours of the cockpit inner areas is black ( I used tyre black to prevent a "too dark" hole...).

To add some interest to this F-4K model, it was decided to separate the nose cone in order to fold in at a carrier deck and show the radar and the wings also be folded. The wing tips were cut off and tips folded. The hinges were made from pieces of plastic and a metal paperclip was used internally for model strength.

Two kits are seen here, at left F-4M and right the F-4K with separated nose cone.

The F-4K got and Extra Dark Sea Grey upper finish and white for the lower areas. 
The white was applied first with an airbrush. Next, considerable masking was needed as the grey extends to the lower leading edges seen below. Masking was done with Tamiya fine masking tape. RN F-4K's had a rather gloss "anti salt" finish, so no need for a matt sealer. 
 
 
The F-4K has "slotted stabilizers" and these are fortunately correctly provided in this Fujimi kit. 

A thick coat of Johnson Future was applied to get a smooth gloss result, ready to accept any decals. This also helps as RN Phantoms were rather gloss.

The tail fin tip RWR fairing. Later in their career, UK Phantoms got this feature and the planes were retro fitted. It carries the Marconi radar warning receivers.

Next the very delicate undercarriage was added. The Fujimi kit parts are fine. 
Cockpit canopies were also very nice. Fujimi provides a separate canopy when you want to show them in the closed position). Here, they were set open and some details like mirrors were added on their inside frames. 

The model got its decals. An old Modeldecal decalsheet was found in the decal "pile". Set # 44 has nice decals for a RN F-4K (or FG 1) Phantom of 892 squadron at the Silver Jubilee 1977 . The plane was operated from HMS Ark Royal with a particular nose marking. It had a huge red chevron and diamond markings. The "R" means the plane is stationed on the HMS Ark Royal. 

In some areas such as smaller stencilling, the very good Fujimi decals were used. 
..
Finally, a scratch build Ferranti radar section was added to the model. The radar disk was covered with fine bandage. (later on, a small update to the F-4K was made and a very small fairing added to the lower section of the nose cone; this was not put into this model). 

Also note the "raised" nose gear leg. It was decided to put this on the model as it is a very distinctive feature of the Royal Navy F-4K. It gives a "higher" angle of attack at catapult take-off from the smaller RN carriers. 

 Another couple of views. Note the back walkway panels and folded wings.

A very nice addition to the collection.

Have a look at the Royal Air Force Phantoms 1/72 models here...