pafarmer, rebuilding an older machine seems like a good option to me (if the price is right). Wondering what series your current 6's are, how long did you run them, and how many hours do they have. Downtime becomes a big deal when you have several employees and and can be a major factor when deciding whether or not to upgrade equipment.
And downtime caused by new technology (tier IV) only exacerbates the problem.
On that note PAFarmer, there will be no mandatory emission upgrades on the CCR, correct?