hunter49,
Cool idea for a scratch built project!
I had the pleasure to work on a lift crew that used a Demag CC 8800 crane with a 1375 ton weight! It was brand new and featured counter weights riding above four giant wheels producing virtually zero turn radius for such a huge machine.
On the subject of searches try Demag, Manitowoc, Liebherr, American, Link-belt, and Terex for brands and search Sterling Crane for a company site.