Ah! I understand now - the mention of Ark Royal made me think it was the RN Phantom kit!
It is possible to convert an F4J to a the FG1 or FGR2, but it's a heck of a lot of work, as I found out (before the Hasegawa kit was released) in both 1/48th and 1/32nd scales.
The nose radome is similar to the 'J', but everything else is different! The fuselage and intakes are wider, and fuselage deeper at the rear, with a pronounced downward sweep on the underside, forward of and leading to the jet pipes. The latter are of wider diameter, a different shape and shorter, and then there are many detail and internal differences, plus the extended landing gear, auxiliary doors top and bottom etc!
It's much easier to get the Hasegawa kit or, if you want to save a bit of cash, one of their RAF FG1 kits, which were ex- Royal Navy birds taken on by the RAF when the Navy stopped fixed wing conventional jet flying.