[Boater Sam]

I have one on the go at the moment. A proper sized set, everything is to a large scale, including the cord drives.

I thread them as per the diagrams, holding the cords in place on the pulleys with masking tape, without the springs, until I have everything in place and thread the ends into the tuning drum.
Taking all slack out, I tie ends to the spring as close as possible before hooking the spring on.
If you have problems getting the tension, tie temporary knots to the springs, hook it all up, adjust the tensions, then tie better knots. Rehook the spring.
Sometimes with long cords, I hook it all together with the cord off one pulley, resting on the pulley axle, and then lift the cord onto the pulley last thing.
This gives a bit more tension.
I use knitted Necklace Bead Cord, 1mm, from China and pre-stress a length over night by hanging it with weights, not that it stretches much at all, but it takes the curl out. Its cheap, it takes secure knots well and doesn't slip.
Nylon fishing line is a beggar to tie knots in that stay put.

Always remember that there is/was supposed to be a blind guy who used to re-cord sets!