I don't think it is a invite, it is a deal where the teams sign up for the series, they were looking for 8-10 guys making a commitment. For races where one of the commited drivers can't make it then they go to the part time guys.
who have stated they can't make all the events but would like to race a few of them
email me or call me if you have any more questions. (you should still have all my contact info
Dean