I thought I would be clever mounting the gas block. I eyeballed it first for alignment. My barrel came with rubbery plastic caps for the breech and muzzle. I used 3 fingers to cover the gas tube holes and 1 of the roll pin holes on the gas bock then covered the last roll pin hole with the nozzle of some compressed air. I held the muzzle cap against me and when the breech cap was blown across the room I knew I had a good alignment. So I used locktite on the clamp screws. Then I go to torque my barrel and remember the wrench I bought fully encloses the barrel and won't fit over the gas block....so I had to decide whether to return that wrench for an open ended one or just take off the gas block. I decided to just take off the gas block.
When torquing my barrel, I wasn't sure I trusted my torque wrench so I set it to 20ft-lb. first. After that I could see I was almost half way between two gas tube holes and the hole on the upper. I set my wrench to 25ft-lb. That barely moved it, so I loosened the nut some and set the wrench to 30ft-lb. That still wasn't enough, so I set it to 35, barely moved it. Loosened the nut some, set it to 40..still not enough 45...not enough 50..almost. 55ft-lb. aligned them and I checked with a drill bit (3/16 I think). I then peeped through the receiver and saw it looked good, although I might have needed a tiny bit more, but I thought 55ft.-lb was already pushing it, even 25ft-lb below the upper limit. I probably messed up on my tighten-loosen cycle, but I guess we'll see if it blows up in my face.
Then I decided I could try my compressed air trick again by capping the muzzle and putting one of the plastic dummy rounds which came with my stock in the chamber. I was getting the rounds to blow straight up. Tightened down the block...then the gas tube would not go in without putting pressure on it...so I loosened the block again until the gas tube would go in without being pressured and apparently without bearing against the side of the barrel nut holes. Took me a while to get the roll pin holes on the block and tube aligned. Lubed the roll pin and that thing when in like butter. Apparently the trick to getting roll pins in is a bit of lube.
So I pop in my charging handle and bolt carrier assembly and try to determine if it is dragging on the gas tube. I am still not sure. It didn't take much pressure pushing it in and pulling it out, but I could feel a bit of drag as the bolt cammed closed on the chamber. My gas tube is coated black and it didn't appear to be getting nicked.
the Free float tube top rail was a really tight fit against my upper receiver's top rail
The directions for the flash hider said to hand tighten and then turn at least 1/4 turn and then until the upper cut was top dead center. When when I hand tightened it, it was almost center. I used a pretty long 3/4 inch crescent wrench and turned it maybe 3/16 of a turn before the top hole was centered. I didn't see how I could possibly get another full turn out of it, so I left it there. Brownell's instruction video said there was no minimum torque value....