As SPadge said - on the left hand side (as per pic above) there should be a screw - the colour of this usually helps in identifying the ecu level.

There's L1 (3dr and RS500), L6 (2wd Sapph'), L8 (regular non cat' - early 4x4 Sapph' & cat with lambda - late 4x4 Sapph') and P8 (Large turbo EsCos)