Distributor Orientation

[Gameparker@cs.com]

List,
in the process of reassembling everything after an engine rebuild and my one 
fear is prompting me to ask this question.  How does one ensure that you don't 
place the dizzy 180 degrees out of rotation?  Is there a way of making 
certain  by looking at the valves and the rotor?  Or is the "test light" method 
I've 
heard about my best bet?
Thanks All!
Geoff
74 TR6