If the creditor/collector gets a judgment against you (and it probably will), then it can seize any assets that are not exempt. An individual is entitled to keep one vehicle worth no more than $2,400 each (this exemption varies by State jurisdiction, so if you move, the exemption may change for better or worse).
As for the "piece of machinary," that would be fair game.
And, yes, they can garnish your wages.
Note: it's actually 6 years to sue on the contract and get a judgment, 7 years on your credit record, but if the creditor actually gets the judgment, then that judgment is collectable for 20 years.
I'm not trying to promote bankruptcy to you, but a $300,000 debt is pretty substantial, so you really should carefully consider the bankruptcy option. Bankruptcy attorneys give free consults, so you really have nothing to lose.