As for costings, I would be very surprised if there were not multiple linked spreadsheets at HR, complete with macros, that can and do calculate "what if" scenarios for various combinations of wage and allowance changes at the push of a button.
Six months to do costings? Six hours is more like it.
It would even be a good idea for the union to build it's own model of engineering labor costs, it isn't that hard. You just have to add in super and workcover and makes some guesses about provisions for annual leave, training, etc.