I've read all over that 6.5 magazines should fit in the standard AR lower (in this case for feeding a .224 Valkyrie upper) but the PMAG 30SPC 6.8x43 magazine isn't even fitting into the mag well - what am I missing here?
(Edited to add - Primary Arms refers to it as the "Magpul PMAG 30 LWRC Six8 Gen M3 6.8 SPC AR-15 Magazine" - did I just get the wrong mag?)
(Second edit - just received the mags that I bought with my upper from PS - aaand they fit just fine. I guess it's that Magpul PMAG?)

The LWRC Six8 isn't a standard AR. Mostly a little wider, hence the mag not fitting.

This.  Those PMAGs are designed for LWRCs Six8 lower, which utilizes different dimensions than a standard AR lower.

Also, I’d change your title.  You’re utilizing/needing 6.8 SPC mags, not 6.5.  They aren’t the same thing.

you got the wrong mag.  

keep it and get a LWRC 6.8 SPC rifle to use it with!