I am having trouble cranking after hot engine stands for about 15 minutes.  When the engine finally cools, it will start, but runs rich and seems to skip.  Heavy carbon deposit evident in tailpipe.  Last time the problem was the Hall control unit.  I installed a cheap one from the local parts house.  Parts house has changed to another supplier and their computer says to be sure to install the proper unit.  Therein lies the problem.

The unit currently installed has no numbers on it.  The Bentley says that "Two different types of Hall control units can be installed." (Fairchild or AEG).  Does this mean that either will work?  How can I tell which one I need.  84 Vanagon Digijet.
George