When I get back from work next week sometime I’m going to start going through my raw aluminum lower and start fitting parts. I only had it a few hours before I had to leave for work. I tried fittings Phase 5 308 bolt catch, it seemed to fit okay, but the set screws (that replace the bolt catch pin) they sent with the lower didn’t want to thread in easily. I didn’t want to force it, so gave up. I’ll chase the threads with a tap when I get home and measure the set screwthread pitch to make sure they match. I believe someone, maybe Dilligaf, said they were 4/40 threads / set screws.
I’d recommend anyone with a receiver set check all the home sizes / threads before starting to assemble it. With correct size drill bits (or identify framers) and bottoming taps.
I also tried a Strike Industries .308 polymer ejection port cover on the upper. It fit quite well, but the detent just barely grabs when closed.