Ok, I know this is stupid but before I buy a pistol lower, I want to make sure it's correct. I bought this on the EE months ago and somehow deleted all my PM's so I can't ask the seller.....and the ad is of course gone by now. PWS website is not helpful as I think this is an older model.
Any help appreciated.....

PWS upper in 300blk. with 4 position gas block. Barrel appears to be roughly 12".

This is supposed to be a pistol upper but it seems too long and all their pistol uppers have 3-position gas blocks....or so I've found anyway.

So, do I get a pistol lower? Thanks for helping.

If the barrel is less than 16" then you would want a pistol lower. If the barrel is 16" or greater or 14.5" with a pinned and welded flash hider or comp then you can have a rifle butt stock.

Thanks. I figured as much but wanted to be sure.

The only thing that matters is the barrel length.  That's what will get you arrested if you put the wrong lower on it, so put a pistol lower on it.  You can whip out the old tape measure to be sure, but I'm guessing that's a 12" barrel.

I'm looking at the gas system and I could be wrong but that sure looks like pistol length by where the gas block is.

Yep (mostly) 300 Blackout uppers are pistol length gas system