My home organ uses very fine steel cable between the keys and the pallets. This is very fine stranded flexible cable covered with thin plastic as used in model airplanes. It is about 0.8mm overall diameter. Look for "control line model airplanes".

The keys are about 500-600mm long and pivot at the far end. The pallets sit straight above the keys and the cable runs straight between them. No need to tension anything, no stretch. With an organ that small you don't need very wide channels so you can keep them narrow enough so you won't need rollers.

It is even used in large organs. The organ in the cathedral in Brussels uses "wire" between the main part and the 2 separate pedal towers.