Allis Chalmers crawler information requested

Hello to everyone ! This is my first visit to this discussion board. The reason I stopped here is that I have located an Allis Chalmers crawler. What I initially mistook for a Caterpillar, upon closer investigation turned out to be an Allis Chalmers. I don't know anything about A-C crawlers, or any crawlers for that matter ! However, I have wanted to purchase any kind of crawler for restoration. I have yet to discover if this machine is for sale. Again, not knowing anything about this crawler, the only indication, other than "Allis Chalmers" on the front of the radiator, is the letter "M" on the side of the radiator. I have included a picture (which was difficult to get as can be seen by the overgrowth) and do have a couple of more if anyone would like to see more. Can anyone give me any information about this model or some idea as to the value ? Also, what is the large attachment that encircles and goes above the crawler ? I will be gone from April 2nd through April 22nd and will answer any e-mails when I return. Thanks for any help !!