Ok. Let me see if I'm understanding correctly.
1. There are 2 arms (upper and lower).
2. On the lowers the bushings are mounted in both ends of the arm.
3. On the upper, bushings are only mounted in the frame end.
4. On the axle end of the uppers, the busing is mounted in the axle housing.
This is what I thought originally, and why I wasked the question originally. Most of the rear arm bushing sets (Energy Susp, Prothane, etc) have 4 pairs of bushings. I'm trying to figure out if the 4th pair fits in the housing or its extra and I need to get the bushings specifically for the housing in addition. If no one knows, I'll just give the vendors a call.