Happy to help! Especially when I am clearly helping the Mom of the Decade! Come on! A mom making a Conjuring music box replica for her horror movie fan son? My mom was too busy throwing out (trying to throw out!) my Aurora monster models to do anything like this!
1st: read the whole thread. Later on I scrap those original movements and buy two new movements on eBay meant specifically for animating music boxes. I stripped the gears on the first two! Here is the movement I used for both the mirror and the head:
http://m.ebay.com/itm/250881930297?txnId=1363738773015
The bent rod they use to move the head of their figures is useless to us, sadly, as it is too big to fit in the box as is. The motor is good and strong, though!
2nd: you are correct that the rotational motion of the music box tune drum has to be converted to the bobbing motion we need for the clown's head. This is done by adding a cam and a cam follower. The cam is like a flat, three- or four-bladed propeller. The cam follower is just a brass rod, hinged at one end, and arranged at the other end so as to rest on the edge of the cam so that it drops down into each "valley" and is pushed up each "mountain" as the cam turns. Think of the cam as a starfish with only 4 arms; as the starfish rotates, the rod traces the edge, dropping down into the gaps between the arms and then slowly forced upward along the edge of the next arm, up over its tip, and then dropping down again into the gap between this arm and the next. The clown head sits on a post loosely and as the rod rises and falls it pushes up the head with each upward movement. The head is allowed to drop back down as the rod drops into the next "valley" in the cam.
I will try to post more photos but the box does not lend itself to disassembly to get good photo angles.
One more tip: my clown head is too big relative to the screen used one. Sculpt yours a little smaller and the movement will be better.
Ask any questions and I will try to help as much as I can!