Tubes Through Their Skulls (1970)

The four Burkhead brothers -- Juke, James, Peyton and Riley -- dig up a friend's time capsule, only to realize that it holds secrets intended for a source hellbent on springing their captive figurehead free. As the brothers, along with their partners Nasty and Cheryl, get wrapped up in another round of cybernetic horrors, the twins begin to lose themselves mirroring the other.