Script to switch to Quark 7.1 Project to Single Layout Mode

I’m trying to make a script that will switch a Quark 7.1 project to
Single Layout Mode.
I can’t get the check box to check.
Here is what I have.

set downArrow to ASCII character 31
set theTab to ASCII character 9

tell application "QuarkXPress"
	activate
end tell

tell application "System Events"
	
	tell process "QuarkXpress"
		keystroke "y" using {command down, shift down, option down}
		delay 1
		keystroke "p"
		delay 1
		keystroke downArrow
		delay 1
		keystroke theTab using {command down, option down}
		delay 1
		keystroke theTab using {command down, option down}
		delay 1
		keystroke theTab using {command down, option down}
		delay 1
		--Need the keystroke to check the checkbox.
		delay 1
		--keystroke return
	end tell
end tell

Any Answer?