Royal Navy with F-8 Crusader instead of F-4 Phantom II

[Yellow Palace]

Only if the ammo belt feed chute runs were altered - the Crusader's "gun problem" was actually the belts jamming in their feed chutes during high-G maneuvers.

If you were changing from four Mk 12 cannon to two Adens, you'd need to redesign the ammunition feeds anyway.

 

[Rule of cool]

Just the question: Has the RN or USN ever operated a carrier fighter jet on a ship so marginal?

I don't know if they have, but you can see why they wouldn't want to.

It's just asking for a crash rate so high it would attrit the aircrew and aircraft fleet down to below a sustainable number appallingly quickly.