Hi Ian.
Yes those are the correct parts which you have linked too, but to honest both those steel pipes are quite thick & robust I doubt you need to replace them, what you may need to do is rub them down treat them and spray black all in situ.
I have two of the first pipe in the shed and they have been there for years now, doubt they will ever get used one used & one new.
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it will most likely only be surface rust, so double check before spending a huge amount of money on these parts.
Regarding your key drop MarinaBrian and or Jamie a PM I am sure both would be able to help with your key problem.