The fuel stabilizer actually separates from the gasoline after you let it sit for a while and forms a film on top separating the air from the gas, preventing the gas from oxidizing and picking up moisture from the air.
For future reference:
I went ahead and emailed the additive manufacturer.
They said the additive is indeed alcohol based, and the lead substitute in this case is potassium, which while it is not recommended for cat converters, should not cause serious damage over a single tank.
They recommend driving it off, and not doing it again.
I might siphon the ...
Those lead substitutes aren't one class of substances. Some have metal-organic sulfur compounds in it which are bad for the cat. Some haven't. Yours seem to be alcohol/butylether mostly, which simply increases the anti-knock rating.
The latter class of substances is most common and does not hurt the cat at all.
Use just regular Sta-bil (or whatever fuel stabilizer you want to use) in a concentrate which is good for a year. Do as you have in your check list and run your small engine out of fuel. I've had no issues with my small engines when I do it like this, even with leaving the fuel in the tank for the next year (Sta-bil treated, of course). It's what I recommend ...