Yes, with the LH4000 dual-tube head you should plug both cords into the pack, so that both tubes fire, giving you a shorter exposure time at the same power, and so that you can use the fan and modeling light. For instance, if you plug one tube into one side of the pack set at 800 W-s, you'll get the same light output as you will with both tubes plugged into the same side of the pack, but with two tubes firing the exposure time will be half what it is with only one tube.
The LH4000 can handle a maximum of 4000 W-s, so if you have two P2000D packs, you can plug one cord into the 2000 W-s socket on the back of each pack for maximum output. There have also been some single 4000 W-s packs that will give you that much power from this head, if you need it.
With the LH4000, you should always leave the modeling light turned up on maximum, so that the fan is at full power, depending on which fan you have. The earlier fans change speed with the brightness of the modeling light, and the later fan has a constant speed, independent of the modeling light.
Norman is very good about sending manuals and such, so you could e-mail them, and they can probably send you a photocopy or a current manual.
