There are 2 kinds of Billys. First, there are the Bilstein Sport. The other kind are the HBE dampers which are still yellow but have no protection gaiters on them. They were only available from EB Spares as a set of four.
I remember they were advertised only for the TS. I couple of years ago, I swapped the dampers on a TS for those on a 3 litre. The customer wanted the HBE kit on the 3 litre. End result was the TS was really nice and firm yet yeilding, whereas the 3 litre was just a bit too soft. It wasn't worn or dangerous, it just wasn't as composed or stable as it should be. I think Alfa set them up differently. The TS was always a bit softer and playful so it could be unstuck with its relative lack of power. The 3 litre was set up for what it was, a serious high performance sports saloon. That's my tuppece worth.
I have Spax on mine right now, but I think the Eibach rear springs are a little soft, so I am considering a change to a Koni kit or simply RS Racing rear springs. I think I need dampers too as I seem to remember the locating threads are corroded and worn as they are now very old and not as firm as they used to be. And the adjustment machanism has long since stopped working (just as well they are on a very firm setting).
