All Canadian MkII helmet liners are marked somewhere. All liners would be made by VMC(Viceroy Manufacturing Co.)

The size is usually marked on one of the fibre braces that make up the crown of the liner. They can be stamped anywhere on the braces so removal of the liner may be nessessary. There will also be a C-Broad Arrow stamped in white.

And no, Mk.II liners are not one size fits all...several sizes were manufactured.

If the price is right I would still buy it, liners are not so hard to come by. Securing bolts and cross pads....thats another story.