yes,it has been installed later.it seems that it has been a fixbridged before.
the trem works well concerning tuning stability.(its the older wilkinson model with an adjustable spring at the tremolo bar). but i think there are better trems on the market which feel smoother and sound better when the whammmy is rocked.
i am thinking about replacing it with the tremking unit,but there seems to be some quality lacking with it.i hope that they will produce a tremking II soon,where all the quality issues are fixed.the idea of having a fixbridged and a trem in one unit and changing it just by the movement of the whammy bar is a nice one. even better than the tremol-no or something.