Steve Earle who runs both the Monterey Historics and the Wine Country Classics in Sonoma hand picks all the entrants for these venues.I know a guy who has a vintage IMSA Chevy Monza but they wouldn't let him run because he has a modern fuel injection system on it.
They get pretty picky on who makes it and who doesn't.
I know another family who has a beautifully restored '69 Z/28 (one of the sharpest T/A cars in exsistance
)and they didn't accept his entry this year...he was bummed!
He has raced this event many times and Wine Country too.The only reason I can think of is lack of space on the grid but like I mentioned,his car has as much race history as most of the others with the exception of the Penske & Bud Moore cars.