i should imagine it is the stage 2+
That's what I have
and what I assume this fella has as there is not a stage 3 box
The new prices are stated below which may help define how much a second hand one is worth.
Stage 1 uses uprated Ford viscous limited slip diff : £495
Stage 2 uses Quaife ATB limited slip diff : £895
Stage 2Plus has shot-peened gears : £1,195
http://www.gearboxman.co.uk/psgearboxes.html