Some things still not fixed.
What ?
Portsmouth Bill
Re the Sea Dart against Sea Wolf blast damage. The early Type 22's/Leander's had Exocet mounted very close to the forward Sea Wolf and suffered no effects.
The Dart loader could easily be modified to take the missile from a vertical stowage and load it out of the doors horizontal. After all it only requires some engineering work and you have a loading room that was designed to take 2 Sea Slug so plenty of space.
Hood
The whole of the design is a what if. So I think that as a feasibility study Sea Dart would have been possible to fit on board. Certainly not cheap but definately possible, after all a new build would be cheaper thana rebuild to this standard. Think of how many Sea Dart rounds would have fitted into a magazine that GW96A would have had. After all a Batch 2 County had 36 Sea Slug and that was with a lot of though given.
I suspect that you should be able to replace 1 Sea Slug with 3 maybe 4 Sea Dart.
You say by late 70's Cruisers would have been out. Personally I agree with you about the history. But the RN built the Type 82 almost 2/3rd's the size of GW96A to try and fit 2 types of missile ie Sea Dart and Ikara on the same hull. So if GW96A had been built would there have been a need to build the Type 82? Might take a look at the Ikara replacing the A turret see how that looks?
However, what is the Cadet training ship in portsmouth, it's a rebuilt HMS Bristol rather than a more cost effective/bigger accomodation RFA.