First off glad you have now become more familiar with the Light rifle than your post a couple years ago on the Colt Forum
I believe that the Light Rifles were made by Saco Defense which until 2000 was a division of Colt. Saco Defense is also the builder of the military's M60 machine gun.
I can't speak for the Light Rifle but I own a Weatherby Mark V (Saco manufactured the Mark V rifles for several years when Weatherby first brought production back to the States from Japan) that was made by Saco in the mid 1990s and the quality is fantastic. I would assume that anything that came out of that shop would be top notch.
However, I question your assumption that everything must be great because one thing was.
I have owned two ULAs in 7mm-08 and one in 6.5x55 with one Light Rifle in 30'06 so I understand both rifles, not just the Light rifle. Plus I helped work up loads for a 300 Win Mag for a friend of mine.
However, a little web search in the articles for the shooting sports "Industry Insider" and other shooting magazine articles, plus numerous websites will let someone confirm the issue with the mftr of the Light rifle for themselves.
Here are some generally agreed on facts even if you do not like them.
No more than 6,000 (could be as low as 4,000) were made with all long actions in 270, 30'06, 7mm Mag and 300 Win Mag
First built was the 30'06 and immediately subjected to a recall with firing pin and trigger issues which were fixed and the rifles remarked with no further issues. In technical and laymans terms a recall is called a "manufacturing issue" by the way to say the least.
Colt changed the mftr specs from the ULAs which are and were custom action tight specs. No commerical mftr is going to build mass produced rifles at those specs and sell them for 1/4 the custom price. So just naive to even think or say that.
Melvin Forbes from NULA confirmed that today and no parts are interchangable. He can make parts though. Colt did not use the Doublas premium barrel that ULA used. They also did not use the Timney or Jewell triggers that ULA used.
ULA only specs for the outside rcvr diameter and weight on his website, so the fact that you have measured your light rifles outside diameter, seen that they are within .001 of the ULAs certainly does not extrapolate to mean that the internal dimensions are the same, as they most certainly are not the same.
As there is a 1/2 lb difference in weight or more, I fail to see how you determined they were the same other than the outside receiver dimension.
SACO was the final assembler as some parts (not all) were farmed out. The spec changes and all of that led to the documented mftring and fitting issues. Most insiders say that Colt had a poor mftr and marketing plan along with the litigation issues. SACO sold the last 1500 to CDNN to recoup the money Colt never paid them. CDNN sold them for $399. That is how I bought my 30.06
You are correct that NULA has not been in business for 100 years, only 20. Hell that is twice the time of half the gunsmiths on this board. Plus totally irrelevant to the issue.
Having served 24 years in SF I am more than familiar with the M60 and its counterparts medium machine guns who were much better. That is why we have adopted some of them, so not sure any attempted comparison means anything, (particularily positive) with the Light Rifle which was manufactured to the changed specs Colt gave them.
Now with Melvin regaining the rights back to his design and starting NULA back up, just how is Colt supposedly going to mftr a gun they do not own the rights to anymore?
Now having said all that, the Colt Light Rifle is a very reasonable rifle in the light rifle category. Especially if you can get one for $600 or so. It is light, reasonalbly accurate and with a follower and trigger change, quite functional. Which is basically what I have said.
Just pointed out a little of the history, whether you like it or not and that parts are not interchangeable with the NULA or even available today from Colt. They will have to be custom made other than springs and nothing is off base from that. Custom made parts cost more, take more time and not every smith wants to mess with them as compared to "off the shelf" factory parts that are normally available. Breaks on a hunt, you are SOL.
By the way, mine was a decent 3/4 MOA rifle and that is all I tried to work up. The 300 Win Mag we worked loads to 1/2 MOA. Very good but certainly not the best or remotely close to the worst factory rifles I have seen.