This sounds like projected upgrades filtered through ‘Chinese whispers’. As you noted for Sheffield, fitting Sea Wolf where the main gun was would be environmentally challenging.
Edward Hampshire provides a footnote source for both items:
Sheffield: DEFE 24/3200, ACSA(S) to DCDS(OR), 5 August 1980 (Discovery lists a title of
Destroyers - Type 42 - RPD 7096)
Batch 4: DEFE 69/1231, Rydill to DG Ships and DGW(N), 12 September 1977 (Discovery lists a title of
Type 42 destroyers)
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I think the problem is that naval research seems to be undertaken by a relatively limited number of people and most published books focus on built ships, there is a smaller 'Secret Projects' movement for warships compared with aviation, almost non-existent for Cold War ships.
It's clear that there is a wealth of material not covered by Brown, Moore or Friedman in the 'classic' texts. Although in fairness plans changed so often and concepts chopped and changed that it must be hard keeping track of everything. This book at least provides the strategical, operational, financial and political background to the naval programmes - something that purely ship-focused books lack.
For example, the Fleet Requirements Committee in May 1979 actually selected the single-ender Sea Dart Type 43 with Sea Wolf, Super Ikara, towed array sonar and no helicopter before it was axed.
Hampshire argues that Type 44 was actually a 1980 reduced Type 43 version using the Type 22 Batch 2 hull as a cheaper alternative which was simply presented to the politicians as a 'new' design with the Type 44 designation after Type 43 had been cancelled.
In another twist the 1978 LTC had 4 Batch 3 Type 22s planned which reverted to the Batch 1 hull length with the Type 23 being based on the large Type 43 hull!
Then the 1979 LTC switched to 22 Type 22 with the longer hull retained for Batch 3, updated Sea Wolf, Exocet successor, two Lynx. Type 23 would then be a similar ship but with one SKR instead of Lynx.