The Little Kong puppet is actually the "long face" Kong model used for the T-Rex battle in King Kong (1933). For this film the armature (metal skeleton) was stripped of its rubber and fur and remodeled to look like a younger albino gorilla.
Merian C. Cooper's enthusiasm for this movie was curtailed when he was told he had less than half the budget of King Kong (1933) to work with, and he had to have it in theaters within six months, for Christmas 1933 release.
Because they knew little about the stop-action process employed by Willis O'Brien on "King Kong," producers Cooper and Schoedsack more or less left the animator alone. However on "Son of Kong" they became involved, a situation that angered O'Brien. Rather than argue, O'Brien would seldom show up for work at the studio, and Buzz Gibson had to finish the animation without him. He asked Cooper to remove his name from the credits, but the producer refused.
One of the scenes involving pterodactyls flying in the far background was matted into Citizen Kane (1941) during the scene where Kane and "friends" make for the beach from Xanadu - this was done to save production costs.