More than likely the tractor set so long it stuck so the guy completely rebuilt the engine.
I have heard stories like this before. The original owner was probably an old man that bought the tractor new and died a few years after he bought it.
The family kept it because it was dads, granddads or someone similar, ran it a little but ended up letting it set until this guy came along.
If I had the cash I would go take a look.
What does a 730 weight?