Sorry my read on your post was that you were proposing a "rip and replace" of Sea Dart with Seawolf. It wasn't clear to me if GSpectre was proposing sea wolf as a supplement to sea dart or a replacement.
My own thoughts were confused to say the least

, that said i was looking for a way to get the VLS system deployed on RN ships by the early eighties, my first thought was to put them on Leanders, but that didn't really seem to work. Then i wondered if they could be squeezed into a Type 42. Continuing that line of thought I'm now wondering if the Bristol could have been refitted with a VLS Sea Wolf system during her 76 refit as a proof of concept, perhaps in place of her Limbo? Only for the Batch 3 Type 42's to include a couple of VLS cells, or possibly a mixed Sea Dart/Sea Wolf VLS system that was developed from what was observed on the Bristol's deployment.
The main reason i went with using the Sea wolf as the missile for the RN to implement a VLS system was that it was already tested. The orginal missile trials included work done on a VLS system, although nothing came of it. I've never heard of the Sea Dart being adapted, or even any trials run on adapting it to a VLS system, if i'm wrong about that though feel free to point me in the right direction.
AFAIK the only place where VLS Sea Wolf could have been fitted on a Type 42 is where the Sea Dart launcher is, that is unless the helicopter facilities were sacrificed.
However, IIRC there was a proposal to fit Type 42 with a lightweight version of Sea Wolf, that used a pair of quadruple launchers similar to the ones that Sea Cat used, but AFAIK they had a pair of Daleks fitted instead.
Could the RN have implemented a Russian solution and put them under the helicopter pad?
Does anybody know if Type 42 was big enough to take the Type 988/Broomstick radar? The Type 42 Batch 1&2 hull is smaller than the Dutch Tromp class, but the Batch 3 hull is larger. Type 42 and the Tromp class use the same Olympus/Tyne COGOG machinery, but they have different power ratings according to their Wikipaedia entries.
At present my thinking is that the RN should have gone the other way. That is it should have bought Broomstick and fitted it to Bristol and 14 Type 42 (with enlarged hulls and uprated gas turbines if necessary) in place of the 8 Type 21 and 6 Type 42 Batch 1 of OTL. The larger hull might be an advantage because it may mean that the hangar and flight deck could be enlarged for 2 Lynx or one Merlin sized helicopter.
If the Type 42 Batch III hull was large enough to take the sonars and data processing equipment I was going to have more Type 42s built in place of Type 22, bringing the total to 36 vice the 8 T21, 14 T22 and 14 T42.
With another 8 Sea Dart systems on order in the early 1970s for the ships being built in place of the Type 21 I thought there was more chance of Land Dart surviving the 1974 Defence Review and it being purchased to replace Bloodhound in the RAF and Thunderbird in the British Army.
The next stage for the RN in the Sea Dart Wank was for GWS 31 Sea Dart to survive the 1981 Defence Review and a VL Sea Dart to be developed for Type 23. The R&D costs would be paid for with the money used for the 1980s upgrades of Sea Wolf.
This leaves the original GWS 25 Sea Wolf with no Type 22s to fit it to (there would be no Sea Wolf Leander refits either). However, IIRC the Invincible class was to have been fitted with 3 Sea Wolf systems, but they were deleted by Lord Carrington because he thought that there would be enough Sea Wolf armed frigates to escort them. ITTL no Sea Wolf armed frigates were in prospect in 1973 so he kept them on the Invincible class.
Re the Tromp/Type 42 power rating my copy of Janes NATO warships handbook give the Olympus stats as the same at 50000 SHP, but the Tynes as lower rated on the Tromp class (8000 vs 9700). Not sure about the Broomstick though... sorry.
I do like your thinking on the Sea Dart/Land Dart... i might steal it for my Chile Wank TL... if i can ever get past writing 1970 that is...