From what I've read, we no longer have to have the restrictors in.
They were only mandatory during the time when leaded, and lead replacement fuels were available to stop the mix up there.
Also, if the pumps were designed to avoid the mix up, then the sizes really should be swapped...
A petrol motor can run with diesel mixed into it, as it needs REALLY high compression ratios, or a flame front to ignite it. Hence, it'll just make the car run really oily, and blow blue/black smoke until it's all gone.
Now, throw petrol in a diesel motor and watch all hell break loose as the petrol pre-ignites, then ignites the diesel, then bends rods as we've only just started the compression stroke... Not finishing it...