http://upload.wikimedia.org/wikipedia/en/c/c2/F-4_3-view.jpg
The F-4 has had many variants, but none of them seem to have had the benefit of using a turbofan rather than the J79 turbojet. The J79 required alot of extra steel around the unit in order to protect the area surrounding the engine from excessive heat. The J79 is a rather large engine running around 38"W by 208"L; for comparison sake the F404 is 35"W by 154"L.
http://www.boeing.com/defense-space/military/f4/images/d4c-36084sm_n.jpg
Just under 1,300 pounds of heat shielding went into the F-4 just because of the J79's heat emitting characteristics. The J79 weighs in at between 3,300 and 3,600 pounds; for comparison sake the F414 is between 2,200 and 2,300 pounds in weight. By refitting the F-4 design to use F404-family engines the weight savings could reach 3,500 pounds. T/W ratio would approach 1:1 using the F404-GE-402's, reaching 12,000 lbs dry, 17,700 lbs wet. T/W ratio could easily exceed 1:1 using the F414's, reaching 12,500 lbs dry, 22,000 lbs wet.
http://www.geae.com/engines/military/images/engines_f414_400.jpg http://www.geae.com/engines/military/images/engines_f404.jpg
How good would it be with F404/F414? If its any indication, the teamwork between McDonnell Douglas and the Israeli Aircraft Industries created a prototype F-4 using Pratt & Whitney PW1120 turbofans (13,532 lbs dry, 20,600 lbs wet; 40"W by 162"L; 2,900 lbs wt) and were amazed by the bonafide supercruise demonstrations.
http://www.aviation-picture-hangar.co.uk/fgr2camo.gif
The empty weight of a J79 equipped F-4S (an extended service life F-4J) runs around 30,800 pounds, its gross weight exceeds 51,000 pounds, and maximum loading runs 56,000 pounds. If you figure the maximum bomb trucking mission could exceed 8 tons, then it lends itself well to increasing overall manueverability performance using that same loadout.
http://www.topfighters.com/images/wallpapers/phantom/03.jpg
According to one source online an F-4S was refitted to have some limited lookdown shootdown capabilities with its 32" Westinghouse APQ-120 (or Hughes APQ-99) fire-control radar and AWG-10B digital weapons control system. The Isrealis took the APG-76 (of the A-12 Avenger program) and mounted it to the F-4. According to the wiki the F-18's AN/APG-65 radar does fit in the nose as proven by Germany's mid-1980's ICE (Improved Combat Efficiency) program. The foreign-used F-4's have demonstrated a good ability to adapt to use new missiles; both the Greek and German F-4's were also updated to fire off AIM-120's, too. The Isreali's use the Pythons and the Japanese use their homebrew AAM-3's on them. German F-4's will be lugging around the IRIS-T.
http://www.fas.org/man/dod-101/sys/ac/f-4x2-s.jpg
The F-4 remains in service in several nations around the world, including Germany, Japan, Greece, Turkey and South Korea.
http://upload.wikimedia.org/wikipedia/commons/thumb/7/79/F-4_Phantom_II_in_flying.jpg/300px-F-4_Phantom_II_in_flying.jpg |