The FVL could come in different sizes, depending on the mission it will perform, but things like engine, drive train, and cockpit components would be the same, common between the two, and swappable.........
I’d have the said the opposite and that the above shows the lessons were learnt. The policy is an accordance with the concept of funding the development of systems and then building purpose designed airframes around them.
In the example you give above of the F-111, the F-14 was subsequently designed around the radar, systems and AIM-54 missile designed for the F-111B.
If RR has an engine in the eventual range of components and systems hopefully the UK could build a suitable airframe around the common items listed above.