Easy thing to misunderstand.
There are two kinds of ridgelines.
1) A hammock structural ridgeline (or more commonly just called a ridgeline) is the ridgeline from one end of hammock to the other. On gathered end hammocks (like the blackbird) that lets you get a more consistent hang each time (you can dial in suspension until the ridgeline is firm but not overly tight) and to hang things on.
People make adjustable ridgelines to use on hammocks. It lets them make that ridgeline a bit longer or shorter to see what setting is most comfortable for them (other hammock ridgelines are set at a fixed length of 83% of the hammock length, which is the most comfortable setting for the most number of people).
2) A continuous ridgeline. That's what you use for tarps. Those are typically 30 feet long or so. They use hardware (dutch hooks, etc.) of various configurations, depending on the person, to wrap around the trees. A tarp can then be hung from the ridgeline and easily centered over the tarp.
Personally, I'd keep the adjustable ridgeline. You could use it on your GT or on any future DIY projects you have. You'll want to order at least 30 feet of zing-it line and some hardware to make a continuous ridgeline for the tarp. Some specific tarp setups can be found here:
The first link addresses an approach for a continuous ridgeline with a tarp.