[...]
It looks like using ethanol blended gasoline in a Vintage Honda comes with a large number of additional risks. [...]
It looks like, it looks like... so far I have read nothing but the usual parroting and I wonder how you can come to that conclusion.
I haven't heard of any problems in my circle of CB owners so far. This much against my expectations, I must admit.
A warning in general: AI cannot think for itself. It's a language program; it collects ripe and green. So realise that AI harvests info from mechanics and noobs alike. Nobody knows and on the internet anyone can present himself as an expert. The recipe that always works, is: create a 'problem' and then present a 'solution'. Success is guaranteed.
I rely on the experts I know on a personal basis in the field like the mechanics I have known and institutions like ANWB, ADAC and leading German automotive engineers.
Here's a simple test anyone can do: submerge a still good genuine Honda O-ring in a cup with E10 gas and tell us what your findings are after a month or longer. I know the rubber used in old vintage (50s) cars may not like it, but the rubbers used in our bikes are of another generation. I have used all kinds of gas in the 46 years that I have owned my bike. The only rubbers I have renewed were the tiny O-rings around the main jets and the floatbowl gaskets. Mainly because I had mishandled them, not because they were 'eaten'. I have renewed the 4 seals between the manifolds and the head, because everybody says so, but... the old ones were not leaking and to my surprise were not brittle at all.
Here's a similar thing. Unnumerous times have I read here the 'advice' to renew the four rubber boots between carbs and head because they would crack and leak. Yes, possibly. But I decided to do the test. After 49 years and 140.000km I have taken them off last spring. All 4 were sound, no leaks whatsoever, not even a beginning of a crack. I noticed they are very robust, quite thick. For neutrality I should add that I park my bike in a garage. On the other hand: my bike has been in the extreme violet light and temperatures when I spent monthslong vacations in Greece and Spain. I don't say these parts cannot be a problem, but not necessarily, just because someone in the internet says so.
My advice: use your common sense and diagnose first. If you don't and just replace no matter what, you cannot tell it was needed or not.