This is a wonderful historic setting and the event promises to be very well attended.
More details from the Castle Howard website:
https://www.castlehoward.co.uk/DB/whats-on-view-4/classic-car-show-2
Important to note that discounted tickets for Exhibitors (£4.50 for the car plus 2 adults and 2 children) must be purchased online before 13:00 October 2nd and arrival must be between 10:00 and 11:00 on the day:
https://classicshows.org/events/the-motor-show-at-castle-howard-bike-1-adult-
When booking online, the confirmation mentions tickets being sent out by post, however, you will receive them by email and can be printed.
They also suggest when you arrive with a pre-written out document containing your contact details (Name, Address, Telephone number and email address) so that it saves time at the gate.
There is a forum post here if members which to discuss plans beforehand Castle Howard Classic Car Show