Chris, if you look back to page 6 of this thread there are some photos of it taken in the late eighties, it was even worse then!
As to the rigidity, the B50 floorpan/chassis has a couple of strengthening box sections all the way along the floor as per the picture below, which certainly help keep things together, but I still get some scuttle shake over very rough roads.
Driving down the A43 dual carriageway around Brackley the other day I was crusing around 65MPH, so modern traffic was whizzing by, but at each roundabout I would catch the cars up again and accelerate past them coming off the roundabout. It might not quite have the finnese of a B20, but for its size it handles pretty well!!
