I have some pictures taken from the dutch forum from someone that build a Liebherr 974.
It's a digger in the same 75 ton class as your Caterpillar.
Normally the tracks can slide seperate left and right, but he build them sliding at the same time. It's not a problem, if you slew the uppercarriage to one side, the weight is to one side and you can slide the tracks in and out without any problems, or lift the machine with the boom.
This Liebherr is build suberbly,build from steel and weighs 50 kilogram, runs on 60 bar and is completely hydraulic ( also slewing and driving), except for the tracks sliding in and out. It has two radial piston pumps with a variable slideplate, so it has load sensing.
The pictures of the under carriage:
I made some pictures of this machine at the Modelshow Europe:
Here some films for a general impression:
http://www.youtube.com/watch?v=a2X3OKDglAU&feature=fvst
http://www.youtube.com/watch?v=vqcYg...eature=related
He went to some shows in Germany and they call it "the mother of all diggers"
I can not tell you any more details, I don't know the builder, but this digger is famous. I hope this info helps.