Welcome.
You're right to be asking those questions prior to purchase, because the 308's don't all play well together.
Be careful because AR10 is specifically Armalite and IS a completely different pattern than DPMS. To complicate things, even manufactures mislabel parts as AR10 just because it's a 308. What lower did you buy and where did you get it. We'll start with that and move forward.
Edit* some info may be redundant. He beat me to the reply button^^