I'm looking for the most authentic military specification and best functioning lower parts kit like one would have purchased in the 80's or 90's.  Phosphate, not nitrided parts.  No extended safety selector (or hot dog, sorry Schmid Tool).  Aluminum mag release catch button (again, sorry Schmid).  

RRA, Luth-AR since they are the successor to DPMS?  AR Discounts OEM mil-spec kit?  

Please don't say SOLGW, BCM, or Aero Precision since those are basically Schmid Tool kits.  They are great, but not completely mil spec.

Uhuh

Colt.

Colt from yesteryear to 2000’s-yes. Colt now- mostly Schmid Tool.  

Let me re-phrase the question: besides Colt and FN, who offers a phosphate coated parts kit similar in appearance to what came on M16A2s and original M4s?

I bought a Doublestar LPK.  All parts are phosphate instead of nitride.  Smaller safety selector thumbpiece as well.

Arms unlimited gets the Colt ones in for a good price.  Currently in stock for $50 without trigger

https://www.armsunlimited.com/Colt-AR15-M4-Mil-Spec-Lower-Parts-Kit-p/spk99796.htm

How about this one then?
https://www.luth-ar.com/product/fire-control-group-m16/

OP might prefer this one however: https://www.luth-ar.com/product/lower-receiver-parts-kit-ar15/

They do look like the ones DPMS used to sell, which were quite good.

KitBuilder, I wondered if the Luth-AR parts were as good as the old DPMS, considering Randy Luth’s involvement with each.

I've not seen them in person; just looking at Google images of the parts and packaging.
If you get them, please share your thoughts.

I had snagged several of the DPMS LPKs a while back, and subsequently started buying SSF trigger groups for all my "standard A" builds.

I bought a Luth-AR parts kit.  When I opened the Ziploc bag it comes in, I was kind of worried because the A2 pistol grip is the same undersized grey grip that comes with Unbranded AR ELG kits. However, the reset of the parts are good.  Every part is phosphate coated, no nitride.  The hammer has an "E" in a box on it, instead of the "F1", "F2" in a box like known Bushmaster and Remington Defense parts in rifles I have.  The trigger pull is actually quite smooth and light.  The safety selector is the correct look, no "hot dog" lever.  The trigger guard is aluminum and is a little loose and rattlely, but that may just be the Remington Defense lower, because my factory Remington Defense R4  trigger guard is the same way.  

Overall, the parts appear very similar to those in older DPMS, Bushmaster, and Remington Defense rifles.  Which is what I wanted since I'm completing a Remington Defense R4.  The pistol grip is trash. It would be nice if all parts kits had the Anderson fat A2 grip, but I had a Remington Defense A2 pistol grip I was going to use anyway. For the $53 plus shipping I paid, I'm satisfied.

Thanks for the review.

Just to add to your review, I recently used a Luth-AR Upper receiver kit and it had proper pinned Milspec forward assist and port door kit was proper aluminum not the plastic junk.

Nothing to do with their LPKs, but my experience with Luth-AR has been very good. I've only bought a few 3 prong flash suppressors and round A1 front sight posts, but the quality on them was perfect.

I've heard mixed reviews on their A1 rear sight kits, but I have no experience with those. I just bought one of their repro A1 pistol grips and I have my fingers crossed that it's better than Brownells... Otherwise I'm going to Specialized Armament.