So I'm a bit stumped, maybe someone can clear this up. I will admit that I don't fully grasp the differences in the AR10 platform.
I spoke with Windham Weaponry on the phone and asked them what type their receivers were. This is what I was told:
DPMS barrel nut and Armalite height receiver. ??? Does that sound right? From looking at the receivers it just looks like the more common DPMS style but the "Armalite height receiver" has me stumped.
Edit: Searching shows that it would be a DPMS High rail that I need?
They probably mean the "high" profile receiver. You can measure it when it arrives. There are plenty of rail options for both high/low.