Well apart from the wing, tail, fuselage, weapons bay and software, as Engines say's it does have common avionics.
However, with the age of the current sensors I'd expect an updated fit long before the RAF would order the A, and the differing roles would drive the fit even further apart s the design offices diverge. The software builds equally diverging.
That leaves the cockpit, seat and core engine. Unless the USAF changes the seat and upgrades to a new AETP engine.
No risk there then....,,
USAF Plans for Radical F-35 Upgrade Reveal Obsolescence
https://www.flightglobal.com/news/ar...te-for-427210/
Exclusive: USAF Weighing Replacement F-35 Ejection Seat