I follow a couple of forums on other web sites and found this bit of information some-what interesting.
Every once in-awhile they check engine size(know as engine pump). I think the last time for the F5000 group was back at Watkins Glen in 2009. All was ok. This was done again at the last event at Road America, below the findings. The maximum size is 305cid for the F5000 engines.
"I pumped a number of group 6 motors this year at the Hawk as well as six F/5000 motors. Only one F/5000 was over at 320cid. I won't say who it was but he is one of your B/Sedan guys!"