We might give this a look as we're based in Norwich - where are you ?
Heard previous good reports about the old Police Gala but never made it ourselves.
Also in Norfolk I can recommend the Skeyton Goat Classic Car and Motorcycle Rally on Sunday 10th May, pre-registered entry only @ £2.
Pre '74 or 'interesting unusual vehicles' - I'd say all Commers / Dodge definately qualify , I just think they're not wanting 'pimp my ride' vehicles.
Held on the substantial lawns behind this village pub. Not a huge event but we've been the past few years and always a superb turn out of interesting classics, guessing at 80 or so classics parked up. Bit of a village fete feel to it all, quiet chilled.
I will look up details of the MG Owners Club 'treasure hunt' which is open to all makes - down this a few times and it's an enjoyable mystery tour through the back roads of Norfolk.