1. Is Mt. Namahana visible from the site of the reservation where the Sesame Street cast stayed?
I don't think so...Mt. Namanaha is further north on Kauai, (pretty much in the middle of nowhere...no easy access roads nearby, etc.) while the other mountains Big Bird and Snuffy found are on Kauai's eastern side. So is the beach where Mr. Hooper went surfing!
It seems as though Mt. Namahana would be obstructed by Nounou Ridge (Sleeping Giant).
2. Does its profile resemble "Mt. Snuffy" enough for the special-effects crew to tweak the shot, without the whole thing looking fake?
My guess is no.
Look at Mt. Namanaha for yourself. If Mt. Snuffy is a partial matte painting, these guys have sure done their homework. The shadows, color and shading match the ones of King Kong's Profile, the Sleeping Giant and Mt. Hole in the Mountain.
3. If not, could the SFX people have filmed a real mountain somewhere else, then altered the Hawaiian shot enough to make the dropped-in mountain blend with the landscape? I've never worked in film or TV, so I'm not sure if CTW had that kind of technology back in '77.
That's hard to say. That's more of a question for Sesame Workshop. And yes, I've asked them about the Hawaii episodes, and they only had the episode numbers available with no in-depth info on where the gang actually went.
Convincing John