As a side....ABI (was) does a couple of guided rides for the various sections, and also a time or two a year does a paid tour of the entire proposed route. I am sure there are deets on the website you are already digging through.
Aside from them. The Atlanta Critical Mass ride (
https://www.facebook.com/groups/AtlantaCM) and participants often do big sections of the Beltline as part of their rides. It would be quite easy to find some information via them even if you weren't looking to join Mass. Sam Fistel/Angel Luis Poventud (hint)
Additionally there is a FB group called Atlanta Midnight Full Moon Ride, or some variation, that does so as well. (not the big behemoth, small group). In a quick look it appears they may not be active any more, but that was also Sam's doing.