I have put a 4x5 on one of those cheap plastic giveaway tripods.....so, technically, yes...
The only plastic on a real Tiltall is the pad on the camera mount.
And yes, it will easily hold a monorail 4X5 of the brands mentioned here.
I completely agree, a Tiltall will easily support a 4x5 and is a great all around tripod, one of the best designs ever made. Even a Star D knock off copy of a Tiltall will work fine, just not as well made as a Tiltall.