Durbin,
Since you specifically mentioned DC-8-71 there may be one more hydraulic system which I overlooked. I am not familiar with the 70 series with CFM56 engines but the DC8-62/63 had a Thrust Reverser hydraulic system powered by an electric pump which I think acted as a back up to the utility system which normally operated the reversers. The reversers were hydrualically powered on the DC8-62/63 and since they are used for in-flight speedbrakes on DC8's I guess a back up was needed in the event the utility system was lost. Possibly the reversers on the CFM56 used a similar actuation and back up system.