Pre 70's rims are too weak in the center. Radial tires because of their ability to maintain traction on cornering at much higher speeds put a lot of stress on the wheel and they were prone to cracking in the centers.
To a point true, but autocross occasjonally will not stress the wheel too much. That said, regular inspection for cracks developing is mandated.
Years ago a friend who raced a Vauxhaul Firenza bought a set of takeoff DTV whels from their race car. These guys had found that the speeds and cornering they were doing every weekend during the season fatigued the wheels. Rogerbrought them through customs with brake dust on them. When asked their value he said old wheels he bought for $60CDN. Each wheel was £400 new. He raced club racing for years. Another Volvo racer broke a wheel coming into our corner at speed where the frost fence stopped him. 4 new wheels for Sunday.
Tire rim spec is generally the median of about a 2" rim width spread. The tread width is based on that.
