I remember reading about and seeing pictures of the small compressed air tank that Jan-Michael Vincent wore on the back of his belt, that was connected to the helmet visor. If you watch carefully he would activate one of the switches on the left side of the helmet to lower the helmet visor and then to raise the visor, the editors simply ran the film backwards. The same principle applied to the machine guns that extended out from the small "wings". Only one of these machine guns actually popped out, but in order to make it look like they both did and to get them to retract, the editors flipped the image and reversed it as needed.