The Spey engines should have made these the best Phantom dogfighters, but they didn't have the slats of the F-4Es and F-4Fs. I suspect the F-4Fs were the best dogfighters as they had slats and reduced weight. Spey engined Phantoms should be superior energy fighters, though... about 4,000 lbs more thrust at sea level!

So... would it be easy to convert this? http://combatace.com/files/file/1365-hms-ark-royal/

It can be adapted. It already was, but the original author requested that it be pulled down. The ini files need a little editing and the files need to be organized a little differently from SF1 (i.e. in different folders).

Does the RAF version work in the SF2E campaign?

If you´ve got the campaign customizer....
Elsewise you have to manually edit the campaign data ini files.

Bummer. Especially since it would seem it would be a natural fit . . . if TW doesn't plan to include future DLC in the shipped campaigns, I won't be buying any more of them.