A neat gun. I like the drop mag on this one which utilizes the standard floorplate.
I bet that the floorplate drops off the extension (non hinged military style) rather than the whole magazine hinging away from the bottom metal as a Westley does.
On the direct bottom picture you can just make out the screw tip in front of the mag. I would think that the extended mag is screwed onto the bottom metal from the top although there is so much metal there one wonders why they would have drilled and tapped all the way through. Westleys screw on from the bottom.
IMO, this is a more simple design with no hinge to make and no need for the horn tip which the westleys have.

I have a spare westley magazine and have thought of building up a 10.75X68 with it - kinda like a 425 light. And no need to open up the action for the fatter cartridges.