It's nice to be able to piece together a Frankenstein from parts you already have but I think your brother shouldn't have settled on the "Abby Normal" brain. I shudder over the thought of an 11.5" barrel with a pinned 5.5" muzzle device. I know it was common during the Clinton AWB but today he really should be looking at a proper 16" barrel or SBR that thing.
Kinda reminds me of years ago (late 80's) when my boss wanted a new PC in his office and I was doing a test run building/rebuilding a few computers around the department. He was hesitant about it but I swore I'd build him something better than an IBM for 1/2 the cost. I did but had so many parts left over from other rebuilds I also put together the worst, slowest thing that still would actually run and set it up on his desk early one morning. Then waited until he stormed into my office. Once he realized it was a joke he got a kick out of pulling it over and over on other supervisors. And he loved his new "build", it was as good as a high end IBM. Anyway, not knocking your build except think he should look a better barrels.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek