If it was the real thing - my understanding is that the only way would be to remove the splash plate on the bottom side and get the date casting number off of it..
Otherwise as far as I know the real '67 and '68 versions of the 610's are virtually identical otherwise.
Big difference in the runner shape between the one shown and again any '610 version - plus as mentioned, the bowtie emblem and a lack of oil fill tube hole on the front as well!