It is actually hard to tell how much hacking has been done on that, since it is a Leisure and Allied Battlezone and not an Atari one. Notice how the step is integrated into the cab? The L&A Battlezone is not the same as the Atari one, and I can't really exactly remember all the differences.
Note, because of the cut down job, I think this is a PERFECT candidate for Mame. Stripped vector already makes it a perfect candidate, modified cabinet (making un restorable), just seals the deal.
I also have a Battlezone Mame in the works, mine has a double decker control panel though.