Originally, the film staring the Wyvren was called Gamera vs Two Headed Monster W. Then it became Gamera vs Garasharp. Then two weird names were written. Gamera vs Leoman and Gamera vs The Icemen from Outter Space. Gamera was also going to have a 'Destroy All Monsters' film with names on the script being Barugon, Jiger, Gyaos, Nezura and the Whale God from 1962. 

Poor Gamera couldn't get a break huh? 
Whale God derp a herp

Whale God