Good evening, I am brand new to the forum and need a little advice/recommendations. I have built several Ar-15 rifles, but I am currently trying to build an Ar-10. I bought a PSA PA-10 gen II completed lowering sale a while back, but by the time I had the funds to build the upper they had discontinued the gen II receivers. I want to just get a stripped upper so I can build it and customize it. I know there isn’t a whole lot of compatibility between different brands in the AR-10 market, so my question is does anyone here know of any other upper receiver brands that would work on a PA- 10 lower or do I need to just start completely over?