Lots of good info. Thank you.Some general knowledge of the important stuff I learned while I was still building one, before May:
I used the CNA colt mag adaptor from TNA, On my rifle (ser# first 200) it fit perfectly in the lower; the upper however was a different story. At the front of the receiver behind the front pivot pin lug there is that flat area of metal and it extends into the magwell area by a few thou (literally, you can see clearly through the pivot pin pin hole but there is the tiniest sliver of metal, so you can see that it is too far forward for the pin). So if you you buy a TNA and maybe others of the same colt drop in style, you may have to sand a few thou off a 3/4" rectangle front face of the adapter from the top.
After building up the receiver into something else; I finally tried the other version of this receiver (that are made in the UK) and I can report that upper and lower fit together fine with the same conversion block, but because of the tight magwell I had to sand the sides of the adaptor a few fractions of an inch (and got it stuck inside the magwell when I became impatient, no matter, it is was planned to be permanently 9mm anyway). If you are looking for the easiest way to go with the colt style adaptor, I heartily recommend the ATRS set for being WAAAAAY less sanding.
Just remember on the buffer too. It needs to be 9mm (or A5) length (unless you want to eat bolt catches every few hundred rounds) and at a minimum 5.6oz (what is in my colt AR) weight but have heard of guys going to almost 10oz. Before finding an A5 length I was planning on making a small spacer in the rear of the receiver extension with a cut down buffer tube+plastic end piece to get the right size, but I’ve heard of guys using aluminum dowels and even stacks of quarters in the states.
Also, I had looked at using a silent (or captured) buffer system, but if you do, you will need a bolt with the weight pinned INSIDE the bolt NOT the ones that have it pinned in to the back of the bolt (like New Frontier Armoury or the ones currently sold at TNA) as they will be too short and probably bust up your lower and upper.
As for functioning, everything seems to function fine(mags drop and retain, bolt catch functions, everything fits together) on Colt/USGI style parts but without a barrel, I can’t tell you 100%
Anyway my gun (before May of course) WAS only missing a barrel so if you get a run done, let me know.