I'm certain he at least voices the eagle. If he did the Quincy cartoon and the first season episode number intro, chances are he did this too. The style's so distinct, there's no way it can't be Jim's. By far one of his weirder animations, not only for Sesame, but just in general.
One or two of the eagles lines sounds like a little like a Jim Henson voice, but the eagle also has lines that clearly sound like whoever was doing the majority of voices in this.
The CTW Archives "first season show content" has five letter claymation segments listed. The E segment is listed as "Henson Claymation", which indicates Jim's involvement (and there was a Red Book post that mentioned that he collaborated with somebody on claymation segments, can't remember the name of the collaborator), while the others are listed as "Clay S", "Clay Q", "Clay U", and "Clay Z" (the only one not currently available for fans to view, and it's not in any of the first 14 episodes). In fact the first season show content also lists a few other claymation segments, most/all of which have "DUMP" written by them. I wonder if those were done by Jim as well (or even if it was the collaborator without Jim).
Looking at these guides, I've seen images from a few episodes where Oscar is outside of his trash can, and it looks like the first Oscar puppet didn't have arms or hands. The original design sketch for Oscar doesn't show arms either, which i didn't really think much about, but all this time I thought that the reason we only saw Oscar's head in the first episode was because Caroll Spinney couldn't fit his right hand into the can (so it'd be impossible to use both hands). And he was already rebuilt by episode 9.
I wonder if the "Brotherhood of Man" clip was dropped after Matt Robinson left, since Gordon is in it at the beginning, or if the clip continued with his parts cut. Of course a big portion of the beginning would have had to have been cut, but there's also the fact that they could have cut the beginning but left in parts where we can see him (most kids wouldn't know who it is). Then again, Gordon was cut from international airings of the Spinning Wheel segment, so internationally that segment begins halfway through the song.