Carracosta is EV'd to OHKO Swellow after Stealth Rock with a +2 Aqua Jet, then enough Speed creep to deal with Base 110's at +2.
Altaria has Ice Beam to chunk down bulky Grasses Carracosta doesn't like, and Flamethrower for Ferroseed (another bulky Grass, kek).
There is no Diglett analysis, as it is Never Used not that common in NU. I just assumed that you would want a set similar to that though. Stealth Rock could probably be subbed out for Double Edge or something. It's main reason for being on the team is to allow Costa to get a near free Shell Smash off using Memento.