Even my impact driver couldn't budge that bolt. Then I realized the wedge and come out just a little, and the nut was trying to bearing on the wedge and the two were fighting each other. All I got for the effort was metal shavings and a mangled nut with torn up threads. Thankfully the threads on the bolt were fine.

Gave it a WD 40 soak and went to the store for a hex nut 12x1.25 metric. They didn't have stainless but the zinc worked, at least for removal. You'll need a couple beefy washers with holes just larger than the wedge on the bolt and another a bit smaller for the nut to have a decent bearing surface. Make your stack of washers. Lightly oil the threads and the top washer surface where the nut will bear. Then with a 19mm socket on a breaker bar the wedge bolt popped right out easy peasy... I think the secret was making that small space in the two big washers, so the wedge could come out as far as it needed to, before the rest of the wedge fell free. (BTW... it was much colder when it worked than when I was struggling, so warmth wasn't a factor)