Firstly avoiding the scrapping of HMS Vanguard in the early 60's.
Instead have her refitted out like HMS Blake, C3 etc and by removing the rear pair of main guns and installing a hanger and flight deck for a section of SeaKing HAS 1/2's
Then in the mid 80's have her again refitted in the same way as the USN's Iowa class with Tomahawk Cruise missiles etc.
How effective would these refits be?
How effective would she be in the 1982 Falklands conflict and Gulf War 1991?
Would the RN be able to afford and run this ship?
Regards filers
To answer the questions...
How effective: In the top 5 world's most effective battleships, that is to say a massive money sink that the UK (unlike the US) cannot afford. All useful missions could be accomplished more cheaply in other ways.
Effectiveness in Falklands war: has 15 inch guns and some helicopters: only real role that can't be accomplished in OTL is heavy shore bombardment and this is not really needed, although it might marginally reduce British army casualties. Possibly reduces naval casualties too by reducing the weight of attack on other ships, but on the other hand it is likely to attract the Argentinian air force and could be sunk with very heavy loss of life.
Effectiveness in Gulf War: totally redundant
Could the RN afford it: Not without a magical money tree, and it would have to be a very fruitful tree for the opportunity cost to be worth it even then.