Nice wrench project :)
It isn't just that the wrenches got used as hammers you know, because you can't get much force on the little thumb nut to tighten the wrench on a nut, it wasn't uncommon to adjust the wrench a little undersized and then hammer the wrench onto the nut to get a tight fit....
Lube the handle nut up *really* good before trying to take it off, the metal behind it is thin and weak....