I love the L1A1. Have done from the first time I saw one as a kid in the UK and that love was only deepened through service first in the Army Cadet Force (from age 13) and then into the British Army proper for 12 years. I was issued an L1A1 for the first 4 years of my service and used and carried one in Gulf War 1. I hated the SA80 for it took away my 'real' rifle and replaced it with something in a lesser caliber with much worse balance. Ultimately, I came to appreciate the SA80 for what it was and begrudgingly accepted it. I would love to own one for old time's sake.
I can't really accept the metric version of the FAL; the stock height is wrong for me, the pistol grip is at too much of a rake, I hate the fixed charging handle, the front sight is a PITA to adjust, the horizontal body locking catch hits my hand when I shoot and the safety is too short to easily manipulate among other faults compared to the L1A1.
I guess I have owned about 60 FAL's in the last 7 years and still own more a bunch. I have hunted with them, shot targets with them and built more than a few custom one off versions. I own them with match grade replacement heavy barrels, have 'em in .260 and .358 Win as well as .308. I'm currently building a suppressed shorty in .308 for use on duty as I vacillate between .308 and 6.8 as a duty rifle.
In short, I love the damn rifle to bits. It is a thoroughly proven weapon that has stood the test of time and can be made to shoot well but it does take a little effort. I am not blind to it's shortcomings as a whole; parts are not really interchangeable like barrels and bolts as readily as AR's. The FAL can be difficult to scope without the right scope mount. Williams QD Pro is THE mount with the Grenadier Precision COP coming a close second. Both are out of production and have been for some years. The DSA is a reasonably decent work around but it has it's own issues.
Why did I not recommend a FAL/L1A1 pattern rifle over the AR? Simply for what the OP listed as his requirements for his BIL, the FAL was not in the running. The FAL is a connoisseurs rifle whereas the AR is an every man's rifle. There is no doubt the FAL is flat out rugged and reliable but they can be so damn frustrating to get to shoot well sometimes, even with all new parts including the barrel, AMHIK!!
I think the 1 MOA thing is a distraction; there are plenty of rifles out there that have the MECHANICAL accuracy that enable them to out shoot their owners. Equally, there are more than a few shooters who can make the rifle perform at its best, even if it doesn't shoot 1 MOA.
The AR style rifle has the ability to be easily scoped, to change pistol grips, stocks, hand guards and barrels. The trigger is often the Achilles heel of the FAL where as the AR rifle has a TON of great triggers available for it. It is a simple matter to mount a bi pod or light or other devices without affecting accuracy at all.
I am not blind to the imperfections of all the rifles mentioned, whether it be price, difficulty in changing parts/obtaining spares, ergonomics or whatever. The OP had a very specific set of criteria he wanted to be fulfilled; given his list, the FAL is not the best solution nor the only possible solution. Personally, the DPMS/CMMG rifles offer the best blend and value for money given the OP's list of requirements. We all have our biases and every well thought out, eloquently argued point serves the purpose of informing him as to possible options but ultimately, it is his BIL's money and decision to make.
As for Jeffery? Well, he suffers from the arrogance of youth for which there are only two possible cures; getting older or sometimes a good ass whupping from what he would prolly label a 'geezer'.......
No, I'm not offering violence towards him, just stating the possibility some older guy may decide to kick his ass when he runs his mouth at the wrong time.
He will learn sooner or (probably) later that he really doesn't know half as much as he thinks he does. I did many years ago. There is no point debating or arguing with him as he is too arrogant to acknowledge there may be others in this world who have done more, seen more and learned more than he ever could if he had two lifetimes to burn instead of one.
BTW, I got up at 0530 this morning to get ready for court so I could testify at the trial of a DWI driver I caught in March when she was intoxicated at more than twice the legal limit. She was also driving without a license, running red lights and stop signs, had an open beer with her and could have killed someone through her reckless actions. This is called doing your job and I expect no approbation for doing it. Jeffery seems to think that eyeballing a few AR's is a cause for all here to kneel down and lick his boots when it surely isn't anything out of the ordinary. Such is the arrogance and immaturity of youth......