is it rusty in there? Have you soaked it good with a good penetrant like PB Blaster for a few days? Obviously you took the nut off the front side....(you never know sometimes).....
If that doesn't work, heat that sucker up good with a torch and beat it out. You're replacing the arm anyways so at worst you'll burn up a bushing.
I've removed a few of these, but all on Arizona trucks, including a couple on the trail where the Arms failed. They fight you but they do come out. It's got that weird bolt head because one end of it sticks into the inside end of the Torsion bar anchor. I'm sure there's several guys that have done solid axle swaps that might have those still laying around. Not sure if I still do.
NICO has a sister site -
www.nissan4wheelers.com. You might find someone there with a couple of those bolts (I still call them bolts) that you could nab.