CPP sells a power assist that is an add on. It uses a control valve and a cylinder as coliover described for the 60's trucks.
They are also quite pricy. I had one on my 56 and did not like the way it handled on the road. It was fine for parking and slow speeds but that was it. You have to remember that it only backs up your original gear box so the steering needs to be in good condition.
I have installed several Toyota PS conversions on TF trucks. They require modifications to the column and steering components so they are not a "bolt in". Mine has been in place for 10 trouble free years.
Fred
