If you have a bolt and nut arrangement, you usually need a torque that is required to produce the friction forces that holds pieces together. In the case with this spool bolt you compress a spring to achieve a preload, a tension that holds the valve spool in normal position. It is not a friction force holding the spring compressed, it is the form of the bolted joint after compression that holds it compressed.
Usually there is a stop for the nut on these arrangements, a shoulder on the bolt for instance. I believe it is the collar #34 in the Shop Manual's diagram that sets the distance in this case. You turn the nut until it "bottoms" against the stop (spring compression is completed) and, if needed, back it off to find a hole for the cotter pin. There is no need to bother about torque specs in this case.