Ok this is completly from memory so here goes:
DC-8 Hydraulic system:
Flaps (largest hydraulic user)
Spoilers (flight and ground)
Ailerons (bad leaker)
Slots (2 actuators per side, bitch to change)
Rudder (hell hole name says it all)
Horizontial Stab/Alt Stab (hydraulic/electrical)
Thrust reversers LONG DUCT(hydraulic actuated/ 12 PSI pneumatic assisted)
Thrust Reversers SHORT DUCT (Pneumatic)
Cargo Door (Douglas Door/Skydrol)
Cargo Door (Rosenbalm/5606)
So in fact all the primary and secondary flight controls are hydraulic. I think the complete Hydraulic system is 21.9 gallons and 12 gallons down to the stand pipe, with 9.9 gallons in reserve. The DC-8 uses a priority valve at 1750 PSI of reducing pressure a valve closes and only primary flight controls are available off the hydraulic manifold.
A large weakness on the DC-8 is the bogie trim compensator. It has no hydraulic fuse and the hydraulic line is under the landing gear bogie. If ruptured it will drain the Hydraulic system down to stand pipe in 3 seconds. It was always said, if you see the DC-8 taxiing with gear doors down your going to have a long day. The controls for hydraulic selection is on the Cash Register which includes 3 positions. Hydraulic pump can be selected from F/E position or Capt's position, however on some models no Capt's position is available.
As far as the B707, I have no idea about that aircraft other than the DC-8 is a better airplane.