Sliding Door Hardware Question

[Wes Bischel]

I was wondering how this sliding door hardware is installed? The sheaves look like they might be installed by drilling into the inside of the bottom rail - or by putting the bottom rail together in three sections (face, middle, back) leaving a slots or spaces for the sheaves. It doesn't look like a biscuit cutter would work due to being too wide.

Or maybe I'm missing the easy installation method.:rolleyes:
I couldn't find anything online or from the manufacturer.
Thanks for any help!
Wes

Or DUH, would one mortise a slot?