Hi all.  This is my first post here.  I've been lurking for awhile and now I need some help.  I just aquired an complete upper in trade.  By way of information the barrel is free-floated.  Could somebody provide me with a step by step to replace the upper receiver.  I want to keep the barrel.  I have float tube wrench; DPMS multi-tool, headspace guages etc. so I should have all I need by way of tools.  Any help would be greatly appreciated.

Also it appears the guy I aquired it from used red locktite on the screw in the gas block.  I think I stripped the alan screw before I discovered it.  Any suggestions for getting it out?

Thanks much,
Turbine

It's not clear what you want to do,but it sounds as though you want to revert back to original appearance(i.e. lose the free floater and gas block?)State your case first.
The cap screw must be drilled out using TiN coated or cobalt steel drills as they are HARD!
Go through with a small one first then one that is the core size of the cap screw thread,correcting any misalignment of the first hole.The thread will just break up whilst you drill.This is not as difficult as it sounds as the cap screw has a little centre dimple to locate the drill as a process of it's manufacture.Remove all the cap screws.
Withdraw the gas block by tapping gently with a plastic(Nylon) punch all round the block whilst the block is wedged open with soft brass wedges(you can make these by filing some flat brass scrap.