If you're building a 1911, study the Brownell's offerings closely.
It's been my experience that the Major names, are NO better than the lesser names.
Early on, I was using Wilson stuff, until I saw the prices start to rise..........Nothing wrong with raising prices if the item is THAT popular, but I started to compare items and using a larger selection of vendors.
I like Clark, Wilson (still) Videcki, EGW, Baer, Colt (who really makes the small colt parts?) Caspian, Essex, Pachmeyer MS hs'gs, and many others. I like Lightened hammers, but I avoid titanium stuff, and all Stainless Steel fire control parts (hammers and sears).......Stainless hammers and sears can't produce the smooth working surfaces of good High carbon Steel.........I can get smoother, more precise trigger jobs with High Carbon Steel, with less work.
All the parts I use will be "Fit" to the gun and then polished re-finished with the entire gun, so the "as received" quality of the finish means nothing to me........I'd sooner have them in the "white".
Re: Tolerances...............I think ALL the mainstream parts found in Brownells meet the std tolerances, unless you're buying a part that requires fitting, which I do. Its common to find parts that will not fit to my liking without some amount of fitting, and thats a good and natural thing........If you mix and match parts from 3 Marlin rifles, re-fitting will be required!
I'm MORE inclined to buy a part that says "some fitting required" than a std part.
Lately, I DO watch and AVOID anything made in China or Offshore, If I can avoid it.........A 1911 is an American Pistol.........the parts should be, also.
In closing, remember that just because the little plastic bag says Wilson,Clark or Mccormick Doesn't mean they made the part.