I have not found my Amsterdam to be top heavy. As djrobbo says, so much ballast has to be added to bring her down to the waterline, the the weight of the upper works becomes a non issue. He is also spot on about the effectiveness - or lack thereof, of the rudder in reverse, and the fitting of a kort is recommended. I haven't fitted one (yet), but of the 7 Amsterdams in our club, only one has a kort, and it is far more manoeuverable in reverse than the others. That particular one was alxo fitted with a bow thruster which helps too.
Peter.