I disagree with removing Rock Slide. Missing with Stone Edge when you need a crucial revenge kill really sucks, and Rock Slide at least helps somewhat with that. Besides, X-Scissor is doing crap damage to Slowbro and Mega Slowbro anyway (it's great for stuff like Starmie, Latis, and Celebi, though). Make it the first slash if you want, but keep Rock Slide there. I also think Adamant is fine remaining a secondary slash. One cool thing about Scarf Terrakion is that it can beat Jolly Charizard X at +1, which some people run in response to Scarf Landorus-T, and you need Jolly for that (there's probably something else I'm forgetting, but I'm kinda writing this in a hurry). I do agree with putting Earthquake on the Scarf set, mainly to help check Mega Metagross (you do 51.1 - 60.4% to 0/0 variants, whereas Close Combat isn't even a guaranteed 2HKO).
I'll try to give more input sometime tomorrow, but I agree with the other stuff mentioned earlier.