That's perfectly fine if your opinion of them doesn't change, however I think it's important that people know not all is rosy with them. I've been seeing instances (and some very well documented ones) of their shens (both in workmanship and poor attitude) for the past five years and don't have enough customer trust to send any dollars their way.
The Knight's barrel extension wrench is compatible with LR308/SR-25, AR-10, and SR-15 barrel extensions. It unfortunately doesn't work with the AR-15 one. I have a Geissele Reaction Rod for that.
If the carrier key material is pushed up against the side of the screw (and not just barely at one small point) it should be OK. It doesn't have to be folded over the top of the screw to be adequately staked. It's difficult to tell from your pic if it's really pushed up against the screw or not.
The biggest visible difference between the LR308 GI and LR308 GII is how much the receivers extend behind the pistol grip. The GII receiver ends the same amount of distance behind the pistol grip as an AR-15 while the GI extends a longer amount (same as AR-10).
Adams Arms may interest you. Not fully released yet though. It has an accuracy guarantee (1MOA), piston system, within your price range, and uses what appears to be the LR308 GII pattern receiver which cuts down on the weight.
To my knowledge there aren't any BYO piston conversion kits for .308 ARs like there are with AR-15's. I do own a piston .308, but if I were building I'd go DI.
Would you mind elaborating on why you're looking to make this a piston-driven gun? Going to DI will make reaching your budget constraint much easier (or allow you to splurge in more important areas).
Yes. You can find those statements from Knight's employees around the net on multiple forums explaining why there's no SBR SR-25 and why they only make 16"> barreled SR-25s.
While browsing SI-Defense's site after D.R.D. linked their new 16" rifle-gassed barrel I stumbled upon a new billet .308 AR receiver set they're making. The interesting thing though, is that all the controls on the lower are mirrored! True ambi bolt hold open capability for a change! I'm not sure how I feel about the itty-bitty integrated/proprietary mag release button though (not to mention you can't make it CA-compliant).
That's very clearly a .308 AR receiver. Look how long the rear of the receiver extends behind the pistol grip area and how long the magazine well is compared to the trigger area.
Yours is LR308 pattern. You can tell by the rear of the upper receiver cut. Yours is curved instead of straight at an angle like AR-10 and SR-25 pattern receivers.