I read a comment above about stock torsion bars in the rear of a Spyder and just wanted to clarify that Spyder rear torsion bars are NOT stock 22mm, in fact they are 25mm aircooled and 27mm watercooled due to the longer length of the spring plate.
This was a calculation made by VW Brazil engineers (aircooled) and then modified for the slight weight increase of the Suby cars.
Many people don't know this, but when dad and Chuck started manufacturing in Brazil, they had to go through rigorous testing before VW would agree to sell us parts directly from the factory. We had to build a test vehicle and VW spent several weeks testing aero, brakes, suspension, etc...
As for the single shear lower shock bolt question, thats why i mentioned not having tested it on a Speedster/Spyder. On a daily driven Beetle they've held up fine (gong on 5-6 years now Id guess) but Spyders are driven MUCH harder than a lowered Beetle could be...