@quantokitty did some good work with the Tunnel Post , and the others about tunnels. Among the hundreds of comments are some good ideas for research or further info, but they're buried among the, "good work, let's get the mobbed formed!" type comments.
I think this is a potential lead that needs lots more research. Sadly, I am not a great investigator, and don't have much time today. Maybe some of you will help or have more ideas.
The FAA
The article in the OP mentions that Dyar's house location now houses the Federal Aviation Administration. Is there a connection there? When was that building built? Any key PG players involved with that organization?

What happened between the 1924 and 1992 articles cited in the OP article?

Were those tunnels actually sealed at some point? When?
The OP article mentions that apparently the tunnels were sealed and links to an AP article that mentions it in passing. Are there news articles about the tunnel being sealed? What construction has taken place in those areas? And if they were sealed,

What happened to those bricks?

One of the most astounding features of the place was the fact that the walls were carefully, even artistically formed of white enameled brick, pronounced valuable by builders.

If those tunnels were sealed, the valuable bricks would've been taken out and repurposed. It's a stretch, but it may be somewhere to look. If there is some architecture or antiques nerd out there- those valuable bricks with an interesting history could've wound up in someone's home or business. If the tunnels were indeed decommissioned.