We don't have all of the information but the copper plates may be the least of his problem.
500 MCM in a raceway is rated at 380 amps at 75C and most terminals are rated at 75C, not 90C. Two of them come to 760 Amps.
If he has them all in one raceway, they must be derated to 80% of the 90C rating of 430 Amps, or 80% of 860 Amps for the pair, which is 688 Amps.
If they are in free air the ampacity is much higher and would be adequate.