Hi Guy,
I’ve just built a Type 23 and have another to build. I’d question the HAS Mk3 Lynx as these started to come out of frontline service even when I was leaving the RN in 1989. I’d stick my neck out and say that by the time you were on the Monmouth that the ships flight would have had a Mk8 Lynx.
You can go three ways to achieve this, you can buy a separate Mk8 Lynx from Trumpeter, you can buy the HMS Kent that has a Lynx in the Kit instead of a Merlin or you could buy Peter Halls excellent Sea Ceptor upgrade set from Atlantic models, https://www.scalemates.com/kits/atlantic-models-atac35022-type-23-frigate-sea-ceptor-upgrade-set--1336547
All of these depend on if you already have your kit and how much you want to spend on the project.
Other considerations are, what refit did the Monmouth get her replacement 4.5, was it a Mk1 or the new Kryton gun? Again I’d recommend visiting Peters website https://atlanticmodels.net/accessories-2/1-350 scale.html to see what you can get. I would recommend his etch set for the Type 23, it far outstrips the kit offering. Being that you’re down under, you could go the whole nine yards and get the Infini set for the Kent, this will super detail you model https://www.scalemates.com/kits/infini-model-im-535020r1-type-23-frigate-hms-kent-f78--1329888
Final thoughts, decals, again Peter can help with these, he does a Type 23 set with all the ships crests, pennant numbers etc but he also does a set of deck markings for the gun damaged areas, worth a look if nothing else. https://atlanticmodels.net/decals.html
This sounds like a sales pitch for Peters stuff, I suppose it is, but the ex RN Chief knows his ships and his products are a go to for modellers, I’ve personally found them to be excellent and easy to use. I’m no ship modeller but I’m always happy with the results of his products. My bottom line is buy once, buy right.
Hope this has helped and happy modelling.
This is my Type 23 build,
Cheers the Woo.