Model A kingpin locking bolt removal

[The Austrian]

Hello,

since the kingpin bushings on my 1929 Tudor Sedan are badly worn on both sides I have to disassemble the front axle.
During the process I found that the locking bolts for the king pins are different from what I would have expected to see on a stock Model A (see pictures). There is a castle nut on the front side and some kind of long wheel nut on the rear side. I was able to remove both castle nuts but the wheel nuts on the rear side are sitting solidly in place (even after heating them up with a torch).
What kind of locking bolt arrangement is this and what would be the best way to get it out of the front axle. Any help is highly appreciated.

Cheers,
Mirko