John -
When you pull the rear brake drums off, you will notice that there is a hole in the rear axle flange (the part that the lug studs are attached to). This hole is there so you can stick a socket on an extension through the axle flange and get to the axle retaining flange nuts- it aligns perfectly with the nuts. Just rotate the axle to move from one nut to the next. Once all are off, the axle slips right out.
As a caution, the bad thing about these non-C-Clip axles is that the only thing that keeps the axle in the car is the press fit of the bearing retaining collar. I've had these fail during hard cornering, and the result is that the axle comes out of the car with the tire hitting the quarter panel. When the axle comes out, the brake drum comes out with it. This results in loss of brakes.... After having this happen the second time on different GTOs, I now put two short TIG welds on my bearing retaining collars to prevent failure. The welds are short enough that they can be ground off easily, but big enough that the bearing does not fail on me any more. Contact me if you have any questions on the process.