So after seeing a couple other ziplines being used in vids; I've decided to make my own. Below you will find some pics and video. Here is the dolly I made.
The bars that the wheels are mounted to are slotted to allow the wheels to move up and down for ease of mounting and dismounting the dolly from the line.
Wheels are recessed to capture the line and prevent the dolly from falling off.
This third wheel is for providing resistance on the line, to slow the dolly if needed.
Here is a quick vid of test runs I did to see how it worked. Now to build a DSLR mount for it.