Make sure you check the gas system. I've read that some (most?) 300BO barrels use a pistol length gas system since it works better for that round. If that is the case for your barrel, you'll need a new gas tube and a low profile gas tube block...Well, it's done.
I ordered an AR-Stoner stainless barrel from Midway, a barrel wrench, .300 BLK dies, a case holder/length gauge, and I picked up some 110gr FMJ .308 projectiles today.
I just need to grab some powder, looking at H110, but it more or less depends on what I can get locally.
I may go ahead and make another complete upper out of the .223 barrel, I haven't decided yet.
My 300BO upper is still on back order so I have no first hand knowledge yet. YMMV