To answer a question on the Golden Dawn Forum, I drew up the following image to show the placement of the Hebrew letters on the Greek Cubical Cross. I thought I'd share it here for others interested in where the letters go.
The image can be printed out, cut to shape (ensuring the blank squares are cut out) and then folded up to form the cross. This can then be used as a guide for painting a more solid construct.
The above placement, which the original Order used, has the three mother letters down the centre of the front, with Fire (Shin) above, Water (Mem) below, and the reconciling Air (Aleph) between them. The two letters on either side of this are the Moon (Gimel) on the left and the Sun (Resh) on the right.
The back of the cross has the remaining five letters related to the planets, while the 12 simple letters, relating to the zodiac, are placed around the sides.
To avoid confusion, note that some modern groups assign the letters differently.