Window regulator help

[Jb70c10]

Searched the forum but can't find the info I need. Trying to install my side glass in my 70 c10 but can't figure out what the lower roller on the regulator goes into. I know the 2 upper roller go into the track that attaches to the bottom of the window itself but can't figure out the lower one. What/where does it go? What does the track look like? Is it a detachable track or is it made into the door itself? Any pics would be great, I'm lost......