Lefty here and looking to assemble one using a left handed eject spare Bear Creek Arsenal upper receiver.  Ordered a left handed bolt, and have a spare hand guard.

Need recommendations on a decent 10" barrel and most importantly mags that feed well.  Also, do I need to mess with adjustable gas block as this will be left eject?

I have 4-5 SBR'd AR lowers so this will just be an upper to slap on one of them as a range toy. It will almost always be shot suppressed.

I coincidentally just did this a few days ago:


Haven't shot it yet but I'm sure it will be fine.  It may not run without a can but don't really care as I plan on using it 100% suppressed.
If you want a 10.5" PSA has them.
https://palmettostatearmory.com/psa-gen2-ks-47-10-5-carbine-length-7-62x39-1-10-nitride-barrel.html
I'm sure it will be overgassed for a dedicated suppressed build though.  Some people don't care if their gun is overgassed as long as it is reliable so maybe you don't do anything.  I personally like my stuff tuned and to run as smooth as possible.

Thanks. Think I'm gonna go with that barrel and an ODIN works low profile adjustable gas block. I like to be able to tune to gas system, especially when shooting suppressed

Internet says C Products Duramag are best choice for mags so I ordered 5.