I have a D3B and the service manual covers the D3B/931B backhoe, which I suspect is similar to the one you know about. The weights of the different parts (boom, stick, etc.) are scattered through the manual. I did a quick add-up and got to about 4,000 pounds without the frame that is permanently attached to the tractor. The side shift frame adds another 1500 pounds.
That weight of 4,000 pounds seems about right. I have a JD 455D with a JD 9300 backhoe that the manual says weighs 2,983 pounds without the bucket or mounting bracket. The Cat backhoe is probably a bit heavier.
It does not give the digging specs for the Cat, but the JD backhoe will dig 13'8" deep.
The 3,000# model 9300 backhoe is a full load for the 15,000 pound 455D crawler loader, and going up a hill the front end of the crawler (with the bucker) will lift off the ground. The center of gravity of the backhoe is probably four feet behind the mounting point when folded up. I realize you will not use a three point hitch, but in general it seems to me that a tractor would need a TPH lift capacity of at least 8,000-10,000 pounds in order for the axles, bearings, etc. to carry such a backhoe successfully.
