I used to have a Subaru WRX, that was tuned to within an inch of its life, running 22 pounds of boost pressure. It was sensitive to octane to say the least.
I spent a ton of time and experiments to see what my best option was. It ran well on 93 octane, but that was very limited in my area at the time. Sometimes I'd have to fill up with 91, which would cause it to pull timing on me. As far as I know, all modern vehicles use a knock sensor to detect detonation and pull the timing accordingly. I've not noticed in my 392, but I bet it does it. It would likely throw a warning light is my guess.
I discovered that all of those small bottles of "octane booster" were total marketing wank and most did nothing at all.
Some research led me to using toluene as an octane booster. I could get it at my local Sherwin Williams in 1, 5, or 55 gallon quantities.
Toluene is what fell manufacturers user to increase octane (at least it's ONE of the compounds used frequently).
After much testing I found that adding one gallon of toluene before filling up with 91 octane would increase the octane in the tank enough to prevent it from pulling the timing at full beans.
Being a bit of a pepper myself, these days I keep 250 gallons of "recreation gas" on hand. I use it in all of my mowers, trimmers, blowers, etc, because it is ethanol free and stores for much longer. With a shot of fuel stabilizer I've been able to store that stuff for two years and still use it just fine. It's 91 octane.
This is a long response to say that you could stockpile some "rec gas" and some toluene to get your 392 to run just fine during the apocalypse.
vpracingfuels.com
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