From my research, it looks like a high rail is the right one. If not, I dumped $90 on the wrong part. I used Apex's description on how to check and went by that reference.
Gas block wise, I think you will get a million different answers on that one. I just went with a basic .750" low profile block. Some recommend opening up the gas port a little in the barrel while you are there. I can't remember what the measurement is. I figure, I can always go back to that later easily enough if short stroking becomes an issue. So far, mine has eaten everything I've fed it just fine.
Post correction. I had my information backwards. The 10 uses a low rail height and I did order a low height rail (DPMS post 2009). FWIW, installation went well and was very easy. The hand guard rail and the upper rail matched together nicely.
