I used to live in Grants Pass, OR. There's a major street there (forget the name) that has a large landscaping business on it.
He has several old small crawler tractors (like in small dozers) lined up inside his fence. I'm talking all metal as in heavy. All looked like they had metal treads / tracks as well. I always planned to stop in one day and look um over. Just never did.
If I had money to squander, it would be to buy and re-build one of those to new condition.