I see now why Thing Beams are so coveted by offroaders. I pulled a beam out of a '73 Thing and it has these extra braces. Is this the only feature they like or is a Thing Beam supposed to be extra heavy duty too?
Rob is correct . The shock towers are reenforsed with channel iron. The ball joints are much improved on the 181 as compared to the bug. They are not only bigger but if you notice they are parallel to each other and not working against each other as does the bug.
The beam is as far as I know the same as the bug including the spring pack. The spindles are definately different and coveted by the off-roaders due to a 2 1/2" raise. There is an old thread here "type 181 parts interchange" posted by myself that may perhaps go into a few more issues of dissimilarity. Good luck. Bob Ingman