Alistair, the Centurion is an excellent design.... you could do a lot worse.
I suppose it is functionally equivalent to more traditional offerings (such as RCOS) the difference being it relies on geometry instead of material mass to achieve stability.
Rolf, nice work on that Newtonian.
If I could make a suggestion; have you considered turning the dovetail plate 90 degrees? It should add a bit of stability if you do.
http://thump01.pbase.com/t4/03/95110...8.WHCINg6K.jpg