Is this one of the seals you're concerned about, Richard (no. 60)?
(Mdina Italia again.)
https://www.mdinaitalia.co.uk/M230219.html
They also have a selection of other seals/gaskets, which might be useful.
That slack kickstart spring rings a bell - I think it may have been mentioned in Practical Sportsbikes during one of their restoration episodes but I can't find anything in my back issues. There is a detailed installation procedure in pages 57 & 58 of that manual I linked you to so have a look there before trying to modify it.