I looked at doing the exact same thing you are.
I was/am going to use a RRA barrel (Douglas I think). The barrel is 1.050 under the handguard.
What I was told is that you'll need to have the Larue barrel nut opened up very slightly. I think the nut is also 1"
I did also purchase a Larue low-profile gas block, and will also have that opened up to fit. I got the idea from Randall at ar15barrels.com. He also sells one that is opened up already and will fit under the Larue Handguards.
Most of the Way Down the PageI think I'm going to have most of my work done with Adco. they will open up the gas block, the barrel nut, and also I can purchase the barrel from them.
I have a 13.2" Larue Handguard, and the Low Profile gas block doesn't fit completely under the handguard, but most of the way. I have the standard A2 barrel on now, but am looking to buy a bull with the Stimulus money.
You can kind of see it here. About 1/2 the gas block is showing.
Hope this helps!
Curt
ETA: Although I REALLY like what comp1911 did.
I may have to look at that more.