There were two terminals for PE in downtown LA: the PE Building (surface and elevated) and the Subway Terminal (tunnel for the Hollywood/Burbank lines). Google is your friend - and so is Wikipedia. With Wiki always check out the sources (I think they're pretty decent on these two):
PE Building (6th & Main): [
en.wikipedia.org]
Subway Terminal (S. Hill @ S. Olive): [
en.wikipedia.org]
Much of the current Metro Blue Line to Long Beach uses the original PE alignment, though of course things changed in access to downtown (into 7th/Metro Center subway station) & at the LB end.