The axles are different. The inner CV is I think 102 mm and uses 8 mm bolts. The outer CV and the stub axle are made together, which must allow a larger CV which will still fit inside the trailing arm. That's the way the cup cars and current factory race cars are made also.
These two pictures show the brace from the main hoop down to the top of the "cup" making up the top rear damper mount.
And although this isn't the best shot, it shows how the brace is welded to the cup from below, as well as the cross brace. The cups were seam welded to the chassis also. You may notice there is a bit of the rear side of the cup missing: that's so the fitting for the remote reservoir for the damper will clear the cup.