Hi Mica,
As you are surly aware, the battery compartment for the 1976 Short body Series I, is located along the the solid neck through area.
If possible, for the Toma_Hawk, I request to keep the neck through free of any cuts for batteries or any electronics (if possible). I am not sure if we discussed this, but I aware from looking at other basses (Series in particular) you guys don't cut through the neck anymore... Just checking to make sure.