OK.....go to http://www.prrths.com
, then the "National Society" link (under the Keystone)
From there, go to "links" (4th item from the bottom)
On the "links", Mr. Brashear's site is the 4th under "Information Websites" (you might get a referral to the "Dementia Wiki" here, and if you get the "internal server" message, my best advice is to just try again later)
If that doesn't work, your best bet is a hardover book, probably the Barnard, Roberts "Triumph" series, Volumes 1 and 4, but these may be hard to find.
Jerry Britton's "Keystone Crossings" site (also accessible from the "links" page), has a number of interlocking charts, and PRR had at least ten plants within Altoona terminal at its height. Britton's site also has a "PRR-talk" feature where you might be able to find someone with other info --- good luck!