I bought the servos at HobbyPartz for a couple bucks apiece and found the doll at a swap meet for a dollar. The doll says 1967 Mattel on the back and I later learned she is a See 'n Say type doll. The hard plastic body was important for a successful installation.
Step 1: Dismemberment
Pop off the arms and use a coping saw to split open one side. Then crack open the other side and remove the guts. Be careful along the way to ensure that everything can be put back together after. I also spent at least 20 minutes trying (and failing) to get the inner workings functional.