The organisers playfully prescribed a cheesecutter and a cravat. The hat was no problem, but the cravat defeated me. I need not have worried. A few women were done up in their Roaring Twenties flapper dresses and cloche hats. But otherwise overalls seemed de rigueur.
One chap had a sparkling white pair with the cursive logo "Austin" handsomely embroidered on the back. "I expect you don't do much work in those," I said. "They're just for show," he said. "I've got some old, dirty ones if I have work to do."
Much of what happened over the weekend at Hampton Downs Motorsport Park, half way between Auckland and Hamilton, was for show. But there was a serious side to proceedings, too. At the third annual meeting of vintage and post-vintage cars, they were competing for the Roycroft Trophy. As one competitor told me, when you get behind the wheel of a car on a race track, the primal urge is to "pass the bugger in front".
The Saturday briefing for drivers set the antic tone. The track is equipped with state-of-the-art electronic signalling but, said Max Jamieson, the clerk of the course, "we're not going to have lights because that's too modern".
Instead, Jamieson explains the meaning of the three flags that will be displayed to racers. Green and red are obvious and if a yellow flag is held up with your car number, he says, "it means that you are losing oil or there's a bit coming off your car".
"You're going to be a busy boy, then," one wag offers to the flag-waver.
In fact, of course, oil leaks and flappy bits are not easy to find among the cars arrayed as if on display. Their owners speak in welters of numbers - compression ratios, valve clearances, oil pressures - that make my head spin but every so often I'll hear a technical expression that even I can understand: "I'll bet she goes like stink," someone will say. One man who complains that "that bloody MG got past me" is advised by an old hand to let some of the air out of his (own) tyres.
The cars cluster together as if seeking safety in numbers: the Austins here, the Rileys there, the MGs further down (most are English marques). I find my mate Richard McWhannell beside the 1929 Austin 7 Dieppe Sports that he built with Joss Campbell. Theirs is one of 26 pre-1945 cars competing (there are pre-1960 and motorcycle classes too). It's part of the same family as the Baby Austin that was my parents' first car, which they had until I was at least 7. "It was the first car for a lot of people," McWhannell tells me. "Big enough for Mum and Dad, one kid and one piece of luggage."
Motorsport has always left me cold, but the devotion on display here is impressive. In the gleam of the spotless enamel paint or the dull sheen of cast-iron engine blocks you can see the tens of thousands of dollars and countless hours lavished on these vehicles.
The oldest is a 1915 Stutz White Squadron Racer, which came third in the Indianapolis 500 as a new vehicle, 98 years ago. It's the size of a king's tomb in a mediaeval cathedral and - as I later hear - accelerates away from the hairpin with a tractor-like growl so slow and low you can count the explosions in the chambers of the 4.8 litre engine.
Equally impressive is David Brock-Jest's 1938 LaGonda V12, in the darkest shade of British racing green. He tells me it's 17ft long and weighs a ton and a quarter - you speak in old numbers when talking about something of this vintage - and the long sweep of its lagged exhaust pipes make an impressive sight. In the first race of the day, it eats up the field, lapping half of it. I show my ignorance by asking Brock-Jest what speed he got up to. "I wouldn't have any idea," he says. "I never look at the speedo. It's the oil pressure and temperature I keep an eye on."
Once, and briefly, I get a contestant's eye view of the track, in a five-lap lunchtime parade open to any competitor or spectator. Wedged in somewhat undignified fashion into the Dieppe Sports, I look down the bonnet at the rare 1958 Austin A35 ute in front of us. And I'll be damned if I don't feel a primal urge to pass the bugger.