i went thru my ludwig photo archives (some via google) for my ludwig pictoral site i'm working on, and pulled some bonham photos. i eliminated all pics that are obvious shadows. including the amber kit due to the fact that lighting can cast ALOT of shadows and reflections from the batter head.
as far as shadowing on the green spkl kit, you can kinda see it in the 1st pic that's from the same gig that there's a outline of a ring.
in the 2nd color pic (presumably from the same gig) you can see a ring. the shadowing from the sun can not make a perfect shadow ring on the head at anytime of day.
i say he cut a clear drum head and made a ring. i hear that's been a studio trick since atleast the 60's. if anyone has tried to cut a circle in a head, its very hard.
i don't think large stickers exsisted back then either, especially for bass drum heads. in the original pic on this post (which i have too) the ring looks like its alittle over the corner of the "G" in ludwig. so its gotta be a ring.
and lastly, the final 2 pics from 68/69 show a ring on the maple kit.
has anyone asked his drum tech jeff Ochletree?