Before the summer is out I'm going to have to get one of these built. I've got a new-in-wrap TRW USGI bolt sitting in my parts drawer for the last 8-9 years, along with a SA USGI trigger group for a speical M-14 build.
How do these new Polytechs compare to the Marstar Norincos?
IMHO they compare favorably having built USGI clones on both receiver types.
I found the machining in the oprod tab channel to be smoother on the Poly and tighter but slightly rougher on the Norinco. The Norinco has better (less obnoxious) receiver markings than the Poly with its ugly dot-matrix Bell engraving.
I won;t comment on the oprod or bolt since you have both parts in USGI ready to replace them.
The trigger group was better machined in the Polytech, though I know M14 doctor prefers the Norinco hammer and trigger/sear citing them being harder. FWIW, on my Norinco, I gashed the original trigger group (actually I gave it away) and installed a USGI one. On the Poly it was better machined and I kept the housing and replaced only the pins, springs, hammer, trigger and sear with USGI and the mag catch with a Sadlak for Norincos from Fabsports.
The Poly barrels seem to be a bit better IMHO, but that might be because they apear to be newer manufacture and some issues were fixed, such as leaving more metal under the oprod guide and improving the way the crown was cut.
IMHO you NEED to replace the factory flash hider with a cast and machined SAI, USGI, or aftermarket milled hider. Period. In my experience more than 80% are crooked such that the sight dovetail isn't perpendicular to the top dead center spline on the barrel.
One more thing I will say, Every Norinco gas system I have seen was useable as-is. The only "junk" gas system I ever saw was on a Polytech where the gas lock had a big casting inclusion in it (e.g. had to be gashed) and the gas cylinder on the same rifle gauged out of spec with too large a piston bore.
I'm sure others will chime in with varying opinions
