Yes, it will.
The Dark Hour Defense 308/A5 13 Position Buffer Tube will work with your Luth-AR Buttstock but will not allow you to collapse your stock all the way forward.
The length of the 308/A5 buffer tube is 8".
Yes. The Magpul PSR will fit on the Dark Hour Defense 308/A5 13 Position Buffer Tube. However, this tube has 13 positions and using the PSR you would not be able to utilize that feature.
The Dark Hour Defense 308/A5 13 Position Buffer Tube will fit a DPMS pattern 308 rifle. Both DPMS and Armalite AR10 rifles can use AR15 buffer tubes and vise versa. When using as an AR10/SR25 build it is intended to be used with a rifle length action spring and a carbine buffer.
As long as it uses Mil spec it will work.
The buffer tube has a mil-spec AR10/SR25 length, ID, and depth. If using for an AR15 build it is intended to be used with a rifle length action spring and a A5 buffer. If using as an AR10/SR25 build it is intended to be used with a rifle length action spring and a carbine buffer.
A5. .75" longer than a carbine buffer tube.