I studied the roll angle of the new Vintage CB750 K0 rubbers and tried to match the down angle compared to the fins on another K0. I rolled the rubbers down so they angled the carbs similar to how it looks on a bike. They actually got better.
The numbers and mold parting lines are even more wacky, but the rubbers appear to work, still nearly as hard as old ones though. I never got the carbs to pop in, I didn't want to risk breaking the K0 carb plate.