Brausch Niemann in his modified and narrowed Lotus 7 based single seater in the 1962 [non championship] Rand Grand Prix.
Yes, easy if you're interested in motor sport history. As you most importantly pointed out, the car only qualified as an F1 machine by being narrowed. It had a highly-tuned 109E engine with 4 Amal carbs, and non-standard brakes (!). I'm not sure whether the scrutineers in Europe would have passed it, but in his native South Africa they liked to encourage the locals to "have a go".
It was clocked at 127mph on the longest straight, and Colin Chapman remarked that it must be the fastest Lotus 7 in the world. He probably thought it was a great joke. It finished 11th (10th on the road) , 5 laps behind winner Jim Clark in a 50 lap race. It also qualified for the following week's Natal GP but retired (quite possibly the engine cried enough!), but does not appear to have been entered for the actual South African GP. Maybe he didn't want to push his luck.
