I've been running a campaign using a mildly Slavic world and Codex Slavorum as a sourcebook. The only trouble I have with it is that the listings for the various gods don't say too much about what would be special about a cleric of, say, Perun as opposed to one of Svarog. I'd really like a presentation of at least the more major gods in the manner of the Gods and Monsters book. I was thinking of going through myself and looking at reasonable equivalents and modifying them a bit to create a rules-detailed Slavic pantheon. Has someone already done this before I blow a couple of afternoons on this?