From the calculator, looks like equal parts 70% and 91% will work almost perfectly to get to 80.64068%. 70% will work; just not very well. 91% will not work. 83%+ is just almost too much (evaporates too quickly), too it seems.
I do have another, really weird question... nothing to do with alcohol. Y'all seem very knowledgeable, and this kinda worries me. I got an old house in 2018, estate deal, guy died in 2016 (vacant 2016-2018) - guy had lived here since 1950. Was a clean fanatic, although not remodeled since 1974, very neat and clean. So a short while ago there's a toilet issue, leak of clean water, not sewage. Still, some rust, mildew, so I figure I'll just toss some bleach on it and wipe it up. Ooops, spilled some bleach. No biggie. No issues. Wipe it up. Then I go into the other room egads, nasty gas smell. Some of the bleach went... somewhere... under the cement floor... perhaps around a pipe... and encountered something it reacted with. Go outside good lord... gag you out there... was a strong reaction. Kinda concerned about what it reacted with. I do not think it was the "normal wrong" bleach and cleaner mixing that people do, as this was worse smell yet did not seem to be as noxious. Blew my nose twice, bit of blood. Fine next day. I was around someone that mixed bleach and cleaner once, the smell wasn't as bad but the effect was worse on me. The nasty smell took a long while to dissipate. And it was worse outside (I have no idea why yet).
I do suspect the old man had cleaned in the bathroom with some kind of dry crystal stuff, as there was some behind the toilet I cleaned up - and that would make sense, years of those crystals seeping around the pipe next to the toilet and piling up under the floor. Dunno something just seemed to worry me about it. I do not yet have access to that area under the floor - something I just noticed - so I have to figure that out, too.