Movable eyes were inserted, the upper lip and teeth were reduced and the tongue elongated, going past the lower row of teeth. This modified costume is also called the SanDaiKaiju (Three Giant Monsters)-Godzilla.
Ghidrah, the Three-Headed Monster (1964)
The images below were captured from the Criterion Collection Blu-ray, found online, and scanned in from books. Some of the images may have been modified to see the textures more easily.