Ok guys, I've tore down the new G8 rear assembly I got and I must say. GM did a much better job on the G8 then they did on the GTO.
First off the half shaft dia is about the same as the GTO but the inner stub axle is much larger as can be seen compared to the GTO inner stub.
They also used a speed sensor in the hub instead of a reluctor ring on the inner stub (big improvement)
The inner axle stubs are the same length on both sides, everything is the same from side to side except the axle shaft (bar) length.
One axle shaft is about an inch longer on one side.
The outer cv joint retains the axle by a snap ring (a hard pull will pop it right out)
The inner cv joint has a large snap ring retaining the cv assembly into it's housing and then another snap ring keeping it on the axle. (remove the large snap ring, pull the cv assembly apart and then remove the axle snap ring to get the axle out)
The axles are 37 spline with a 1.18 dia at the splines.
I'll add more information here when I get the diff tore down to see what makes it tick.
Here is why you have the problem with the inner stubs popping out.
You can see the very small machined landing that the retaining ring has to catch on.
The retaiining ring area can be seen in this photo on the end of the stub.
The Camaro center section is a direct bolt in for the G8.
It bolts up perfect, same width and also uses the same inner stubs.
So all you would have to do is find a Camaro center section and bolt it in.