I've seen these vehicles featured in magazines before...usually they're built on a Chevy Suburban chassis; sometimes widened as well as lengthened. The primary customers are Arab oil sheiks in Saudi Arabia, etc. This model is unusual in the fact that it is a cabriolet. Usually, the Suburban is converted into a sedan configuration and armor plated to the hilt.
I'm guessing either Armbruster-Stageway or Hess and Eisenhardt did the work, but I don't know for sure. I guess I'll go with Hess and Eisenhardt.
Dan