Quoted from sethbenjamin:

Should be the same as on any other sys11 game, very close to sys9 and DMD games. I can send you dimensions tomorrow AM.
If in doubt, taking the head off is safer than risking cabinet damage, and it makes moving the game easier to boot!

Quoted from monkeybug:

Measured mine quickly. 28 and 3/4.

Quoted from supermatt:

Just measured, 28 3/4 all the way from top to bottom.

Quoted from sethbenjamin:

Leaving 1/8" on either side of the head is a recipe for cabinet damage. If it's a beater already, you could muscle it through, but if it's in nice shape, for the love of god, take the head off. It'll take you 20 minutes. I know that seems like a really daunting task if you're new to this stuff, but it is not difficult and you won't wreck anything.
Slide the glass off and lean it against a wall, safely our of the way, on a not-concrete floor. If the floor is concrete, put some cardboard or a rubber mat or a towel down.
Tilt the playfield up (remove the pinballs first if they're in there, which they shouldn't be when transporting a game!)
Undo the connectors from the head to the playfield. On Earthshaker there should be about 4 or 5 big block connectors.
Unbolt the hinges.
That's it. Carry the head in comfortably, and wheel in the lower body with adequate clearance to avoid scraping it up. (some cardboard along the sides might not be a bad idea for protection).