Forget the wrenches, for a while, heat to 250 F and melt beeswax into the front and back of the shaft, and similarly the middle where the shaft goes through the casting. There are no threads, the shaft has a cam to tighten against the wheel. Lightly hammer, in and out on the shaft, when you see it moving in and out, then add your favorite penetrating oil, and put an impact on the wrench surface, left and right, alternately. once it moves free, hammer it tight toward the back, and pop off the snap ring, then hammer the pin out the front, and lube up with neversieze. On to the next one. About 4 hours per wheel, if you pull one off at a time. Finally don't lose/ forget the rail followers, and they like a coat of neversieze, on both sides, too!