The headers of the board below are wired as follows (not quite matching the photo):

2 pin header marked BAT: The +6volt goes to the pin nearest the blue switch. 0v to the other.

2 pin header marked PWR_SWITCH: connect to the on/off switch.

6 pin header:
Pin 1 connect to ground.
Pin 2 to the PC socket and via a 3.3k resistor to ground.
Pin 3 to the other side of the PC socket.
Pins 4 - 6 are unconnected.

The jumpers J1 and J3 are shorted and J2 is left open.

4 pin header marked BUT: Connect to the 2 push buttons. Pins 1 & 2 to one switch, 3 & 4 to the other.

The batteries are 4 "AA" alkaline cells. Mounting of the holder will depend on what is available. I am rivetting them to the box.

Possible parts list from www.distrelec.at (not necessarily matching photos) :