OK, here's the best result from a quick google search. It turned up on a German Indiana Jones site;
"The 'lumbering mass of steel' was a fully functional replica of a German{NO- British - GB} 1917 International Mark 7 army tank used in World War I, designed and built by George Gibbs. According to Gibbs building this tank was the most difficult task of the film. These tanks were thirty-six feet long and weighed twenty-eight tons and only seven or eight of them were built for the First World War. The only one left in the world is located in the Tank Museum in Bovington Camp, England. Since both Spielberg and Lucas wanted the tank to look as realistic as possible, Gibbs built one on the chassis of an old excavator that also weighed twenty-eight tons. The tracks alone weighed seven tons and were driven by two Range Rover V-8 engines, which in turn powered two automatic hydraulic pumps - one to drive each of the two tracks. It also had big bulldozer motors in the back to power the whole tank and guns that actually fired blank charges. Overall, the tank was quite accurate. The only real difference between this tank and an actual World War I model was that the First World War tanks had extra eyeball guns on each side and they did not have a turret that turned around.
For the construction of the tank Gibbs chose to use actual steel and not prefabricated materials such as aluminum or fiberglass. His goal was not only to enhance the tank visually, but also to help it withstand the abuse it would take during the intensive weeks of principal photography. "World War I tanks did not have suspension, so we build ours without suspension also. Because of that, I knew the vibration inside that tank would be absolutely tremendous and would shake a mockup vehicle to pieces. For that reason, I decided to build the tank from steel. Also, if any of it ever broke apart we could quickly weld it back together. As it turned out, the tank went down the sides of mountains and over really hard, rocky surfaces without any damage at all-and I knew then that I had made the right decision."
The tank was built in four months and then flown to Almeria, in southern Spain, aboard a British Belfast plane - one of the largest aircraft in the world. To transport the monster tank from location to location, it was placed on the back of a low loader truck. "We were lucky," said Gibbs. "Shooting went smoothly and the tank only let us down twice. The first time was because the rotor arm in the distributor broke and it took us a day to get a new one from Madrid. The second time, it was so hot that the solder in the oil coolers actually melted and flowed around with the oil into the valves, shattering two of them to pieces. So we had to change one of the engines and that also took one day. I think everyone expected to lose a lot more time, but the tank worked really well." Driving the tank was effects technician Brian Lince, who had to weather the extreme heat and the torturous terrain. "Brian did an excellent job. Being in that tank was like being in an oven, and he was in there every day for nearly eight weeks. We had ten industrial electric fans inside to try and keep Brian cool, the engine cool and the hydraulic oil cool. Not only was it hot in there, but since the tank had no suspension, Brian got rattled around so much that when he came out and tried to take a cup of tea, he would spill it before he could get it to his lips."
To accommodate an elaborate fight scene on top of the tank, Gibbs duplicated the upper portion of the lumbering vehicle and mounted it on an ex-army searchlight trailer towed by a four-wheel drive truck. The eight-ton partial tank was identical in detail to its full-size counterpart except that it was constructed from lightweight aluminum and had tracks made out of rubber so the actors and stuntmen could fall on them without being injured. It also featured 'people catchers' on either end in the event anyone accidentally fell off. In total it took two weeks to film the ten minutes shot at a cost of $200.000 per day."