This is definitely viable, but I question the need for Shadow Claw (presumably, purely for Trevenant and Gorgeist?). I think Brick Break is superior, because it gives you the versatility to break screens, and also avoids locking in to Earthquake against say... Tyranitar, Mega Kangaskhan, 2/3 HP Mega Lucario etc. (I mean, if it breaks Multiscale on the switch, it's done its job).
I also think that Adamant and Jolly are different propositions, and should be used differently. Max speed is fine for Jolly (though you could make the same argument for 302 v 300), but 412 (275) doesn't really beat anything that 405 (270) doesn't equally beat... It might not seem much, but those 5 speed points should be redistributed (for example, with 252 Att / 232 Spe / 24 SpD, Excadrill has a 6.25% chance of surviving normal Gengar's Focus Blast, which is infinitely superior to 0%!)*.
Edit: *I know people here readily grasp at strawmen, so to clarify... I'm not suggesting that a few SpD EVs are suddenly a solution to Focus Blast. This was to illustrate my point that a few EVs can make a difference.