From the picture above you can see that this special tool is essentially a notched ruler that attaches to the splined shafts on the steering box. Weights are positioned in the notches of this ruler to apply a torque.
I replicated this tool by finding a bit of soft wood with approximately these dimensions 30mm X 10mm X 300mm. I drilled a 16mm hole in the centre and then carefully cut along its length – through the centre of the hole – to split it into two parts.
I then held these two parts together with two wood screws, one on either side of the central hole, which can be tightened to improve grip on the splined shaft of the steering box.
Instead of notches on the upper surface of the special tool 116 589 03 21 00, I just marked the distance from the central hole on either side in centimetres. You probably won't need to go further than 12cm but that depends on the weights that you have available.
You now need to find some suitable weights that you can hang from wire off of your newly made special tool. I just so happened to have some wheel balance weights that are conveniently marked with their weight. But you can also thread nuts, washers, spanners, sockets or whatever onto bits of wire or string. This is where your kitchen scales come in handy.