The inlets on the front of the DC8 are for the 4 turbocompressors used to pressurixe the cabin.
The top and bottom inlets visible in the bifurcated inlet feed the turbocompressors. The upper turbocompressor access door is visible just aft of the inlet.
The bleed air from the engines which is used to spin the turbocompressors exhausts overboard from the vent located on the side of the fusealge just aft of the access door. The bottom TC exhaust is just foward of the hose connection.
The area in between the two TC's in the bifurcated duct feeds heat exhangers to cool the compressed air from the TC's.
The only planes to my knowledge that used TC's for pressurization are the 707 and the DC8.
The TC's on the DC8 were extremely noisy in the cockpit, and had a tendency to have uncontained failures which scared the shit out of you as the pieces had a tendency to rip into the cockpit on occasion.
To find the condition of a TC on the preflight one only had to look at the TC exhaust duct and find how much oil from the bearing case had leaked past the seal and run all over the fuselage. I never saw a TC that didn't leak.
They also made strange noises notifying you of their impending doom.
Most of the TC's were replaced with the NASI system on aircraft not receiving the 70 series conversion which did away with the TC and used direct bleed air from the engines.
Plugs were installed in the TC ducts but left the heat exchanger duct open.
These ducts are in no relation to the DC10, or L1011 inlets as they had no TC's.
Here is a photo of the plugs blocking the TC inlets on an Emery 71.
Click for large version
Photo © Andy Martin
The scoops on the L1011 and the DC10 are for PACK cooling.