How can I get the window bounds for "Adobe Illustrator" in AppleScript?
Here's a piece of code that just gets desktop's dimensions and transfers them to another application's first window.
Exchange "TextEdit" with Illustrator's process name and build yourself a Service in Automator (open "New", choose Service, draw "Do AppleScript" to right, insert this code ...).
Give it a shortcut via [ System Preferences > Keyboard > Shortcuts > Services ] and get going!
Hope this helps ...

tell application "Finder" to set myBounds to bounds of window of desktop

tell application "System Events" to tell process "TextEdit"
    set position of window 1 to {0, 20}
    set size of window 1 to {item 3 of myBounds, (item 4 of myBounds) - 20}
end tell