I made it 135.0 x 67.0 for the 'glass' itself, but I don't have a decent vernier here. Measured from the image I posted earlier I got 135.0 x 67.5.

Decent measurement tools and decent computer are both at home.

EDIT : Checked with a proper vernier and measuring the supplied plastic shield (because it's easier to define where the edge actually is) I get 135.3mm x 67.3mm. Shame I don't have access to a travelling microscope at work any more