Originally Posted by
rpenmanparker
That is not correct. It is easy to find slotted cleats that attach to the bolt hole of modern road "clipless" shoes. These anchor the shoe to the back edge of a platform pedal. Then to complete the assembly you need toe clips and straps that mount to the front edge of the pedal. Here is what the slotted cleats look like:
Just Google "slotted cleats road shoes" and you will find these and other available slotted cleats.
If you were particularly intent on keeping your platform pedals for versatility, this is an interesting option. However, it's quite uncommon nowadays. You're probably better off just checking out some inexpensive pedal/cleat systems with road shoes.