Looking at the pic, I think the head attachments points are all one static piece and the rest of the head ports hidden in the torso are just a storage feature for the unused heads. An integrated head switching gimmick sounds like way too many moving parts to accomplish something not integral to Scooby Doo. There also doesn't seem to be enough room to accommodate a rotating assembly.
View attachment 37650
Photo from TFW
That's the one! I thought it looked like Fred's head folded down, and another swung into place and folded up maybe. Every head's base is the same, which is odd if they aren't intended to flip up into the same spot.
"Wheel of head-mastery, turn turn turn, tell us from what head that we should learn...Head number three! And today's head's lesson is..."
"JINKIES!"
"Well, that was entirely uninformative."
"Better than yesterday's lesson, 'help, help, there's no air holes!'."
"Hey, wisdom our time needed, that one was..."