The hole is for drainage I believe, that or for oiling.
From here-
http://www.lockweb.com.au/infoCentreDoc ... dlocks.pdf
I got this
It looks like an ordinary brass padlock. Open it, and look down the shackle hole for a screw. If you see one, undo it, and the core should drop out.
There's no mention of it having a removable core, so I doubt this will be the case.
So, Illusion wrote a good guide on how to construct a tricircle repinnable padlock, although the guide should apply to you lock as well as many other locks similar too it.
Its here-
viewtopic.php?t=10665