I mean, there is a bit more. Like this manifest:
http://karaultheca.ru/sources/krivenky02.htm#413
Though by now, I'm not sure this declaration/document you are looking for was ever finalized/agreed on/published. Volin himself, Rocker and Daniel Guerin state that he was tasked, but their exact words give me the feeling this task was never completed. I'll link the sources later...
Nevertheless, after searching a bit more, I came across this:
https://annas-archive.gd/md5/aab03540c65e18fa209c8c917066dd4a
(or https://annas-archive.gd/md5/c4f363977b87c2ee1cd9035c22ec68ec)
and maybe a couple editions of Nabat:
https://annas-archive.gd/search?q=Nabat+1919
and https://archive.org/details/nabat_klich_proletarskikh_pisateley
I think I stumbled over other interesting articles that might contain further information, but I lost them in the growing pile of tabs. I guess I'll take a brake :D
Dunno if this was of any help so far...