The O bar was an in-beam sway bar for MKIII and MKIV cars that had bungs to locate it in the beam instead of blocks. They were probably shorter than the Passat bars; this bar is 34" long and the Shine bars for the MKIV is 31.5" long.
i had an older version with metal tubes where this one is further reinforced. the tubes ended up snapping open because there was the tiniest bit of slop.
but good-lord was it rigid! it was awesome.
and yea, this appears to be pretty much the same as the O-bar. it was in-beam, just as you stated. it did run the entire length of the beam, minus a couple inches for clearance. 34" sounds right to what i had. it was just short of 3 ft.