To be honest you are going to have to have one hell of a good looking bumper with comparable fit and finish as the ARB to be able compete.
4wheelparts has the ARB #3421410 available for $1298+tax w/ FREE to store shipping. I plan on grinding the bumper not my fender.
I wish you luck but it's going to be tough... I am looking forward to see what you come up with.
Oh - if you ever get some pics of your lifted GX - I will add the picture to the first post of my build thread with a link to your build thread (if you have one).
My Build Thread
BonnerBB's Lifted GX470 - Toyota 120 Platforms Forum
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2005 Lexus GX470 | KDSS | 285/70-17 BFG | Icon Ext. Coilovers | Camburg UCA
Official Build Thread
www.LiftedLexus.com