Hey okidoke,
I appreciate you taking a pic of the cans. I never knew heat resistant clear was available!! As for fuel affecting the silver paint, perhaps it needs more time to cure. If that doesn't work, try running some Rustoleum 2x clear where the petrol spills and leaks are likely to occur. Speedy uses Rustoleum 2x coloured paints on his decks as they don't get affected by petrol.
As for age of mower, a very small window of time for the manufacture date of that machine, due to the adapted 1970's cup start plastic engine cover. 1980 -81. Maybe 82 if Victa wanted as much variety as possible and kept producing alongside later style engine covers a little while. I very much doubt a 1971 160 barrel was fitted due to it having a different inlet port fit the older G3 carburettor.
You are definitely right about this mower being firmly anchored in the very early 80s, 1980 -81 financial year most likely.