Go to the trunked system in the database, click on the site you're interested in, look just to the right of the Site FCC Licenses line and you'll see a little icon. Click that icon to see an aggregate map of all callsigns assigned to that site (in this case, a simulcast cell).
Of course that map is only as accurate as a) the FCC licenses are accurate and b) the correct FCC licenses have been assigned to the site in the RRDB. You can also search for the individual licenses to find their locations.
And as a perfect example of how sites are setup directionally, etc., Butler and Armstrong both have a site on the border of Allegheny County at the same Freeport location. Butler's control channel I can pick up full quieting on a stock antenna with my BCD325p2, Armstrong's.....barely breaks the squelch or many times nothing at all.
The sites I know of are:
102 McCune Dr Butler (Prime Site)
200 Block of Whipporwill Rd Conno. Twp (Butler Twp Tower)
Billsburg Blvd Worth Twp just north of 422 exit from i-79 (Slippery Rock/Moraine Tower)
Shields Road Mercer Twp (Forestville/Harrisville Tower)
Foxburg Rd Rt 58 Allegheny Twp (Six Points Tower)
Russell Road Clearfield Twp just off 422 (Fenelton Tower)
Fairmont Rd Karns City at the Penndot Shelter (Karns City Tower)
Hall Road West Sunbury behind the fire hall (West Sunbury Tower)
Kohlmeyer Rd Washington Twp (Hilliards Tower)
Garvin Road Cranberry Twp (Cranberry Twp Tower)
236 Swain Hill Road Harmony (Harmony/Zelie Tower)
I believe there is a tower on Rt 356 between Butler and Sarver somewhere to cover Winfield Twp and Saxonburg.
Freeport Tower just past the Allegheny County Line in Natrona Heights
These tower sites all run the 800mhz system and most do the UHF paging as well. Most of these towers are "existing" Butler towers but some of the new ones they added, mainly in the northern areas, just run the 800. They are using the towers that ran the old system to do the new uhf paging system.