First I had to place all the Nixies into the tanks, and run a wires through the holes. During the assembling the top parts of the tanks were removed, and the 'laminas' and arms were also not attached to the structure.
Than I screwed the 3 tank bases to the base and soldered all the wires to the PCB. I left little extra length of wire to have some space to flip to the side the PCB panel.
After connecting and testing the clock the next step was to place the remaining base parts and the preassembled 'laminas'. The next step was to solder the neon, power and button wires and closed the bottom.
For the legs I was thinking a lot what to use, and finally I have found these brass legs in one of the local hardware shop.
The final step to place the tank tops and the arms and plug the power cable to enjoy the clock.