Robert, The South Shall Rise Again!
You gave up on the idea of just buying a complete gun? These things are in my opinion a lot more difficult to build than a 5.56. However knowing what I know now the MP10 was a pretty good gun, considering weight, reliability, not tack driving accuracy.
HA! I was going to get that Armalite AR10T-18 but after that gay bar shootout in Florida they all dried up. And the M&P10 too. I had a lower I bought on a lark just to have one so I thought I would do the build. But man! It is really confusing. Now it is turning into a grudge match inside my head; I gotta figure it out or die trying... LOL You know how that goes.