The OEM Duraspark ignition system has a default, non-adjustable dwell. Duration , in this context with respect to the rotation of the rotor button, is synonymous with Dwell. In this case, Dwell never changes, regardless of advance or rpm. The distributor uses centrifugal and vacuum advance to accommodate spark advance. In the OEM setup, the EECU controls the coil spark command from the Pick-up Coil to the Ign Mod. The vacuum advance usually supplements the mechanical advance in keeping with the demand placed on the distributor by idle speed, vacuum, and rpm.
For the most part, the Ign Modules appear to be pretty much the same. Years 73 - 86 appear to call for the same part number, though the engine wiring setup clearly changed over those years.
I've not ripped one of these distributors to pieces, but usually the condensor is somewhere between the Ign Mod and Distributor. I can't say for sure that I've even seen one on my jeep. It's purpose is to soak up excess voltage in the ignition system to keep from frying the points. HEI systems definitely have a condensor. There is a watch-battery sized cylinder on the OEM Jeep Ign Module board integrated with the resistors, so maybe that's it. Yes there's a "PC Board" or rather a circuit board inside that box that makes sense of the input/ouput scheme on all those wires. If you've got a dead one and a torch, if makes for interesting busy work to rip in to one.