Mark, I looked for pictures but I don't have one that shows a 1970 4/4. I doubt anyone will know at your show however. I have shown cars all over the east coast (Amelia, St Michael's, Boca Raton, Hilton Head Island, etc.) and have rarely found anyone that knew anything about Morgans. I think using either the pancake or rectangular one like the K&N will probably work for you. Something clean but with patina. I would simply state that you believe it to be as close to the 1970 factory car as you can get it.
I wouldn't use the K&N that I have however as the K&N logo is pressed into the top and couldn't be masked by painting.
Cheers,
