Hi Sockeye,
Unfortunately, I got the ACT1113 pads but, unlike your experience with your 2005 GS300, they would not fit on mine at the front but would, at least, fit the back.
As I still need front brake pads I've posted to the GS300 forum hoping there will be someone else with the same car as mine with the front calipers that won't take ACT1113 but will take ACTxxxx (whatever it might be).
http://au.lexusownersclub.com/forums/topic/12416-which-akebono-ceramic-front-brake-pads-for-2005-gs300/#entry45162