Honestly use a bigger hammer. Something smooth faced around 36-40oz...should knock it loose and allow you to finish the job. Hit that unpainted flat part. You need the metal to metal “shock” to get that taper joint to give..
One of the latest TFL video features a g wagon, JL rubicon and 4R trd pro. They said they brought the top of the line most capable vehicle from each manufacturer...just watch it for entertainment value.
I was just guessing. I am sure benc will be able to answer the specifics. Maybe the top part is two piece like a shell and the bottoms part is one piece? I dig it...it almost look like factory steps but with slider function.