Plugs, wires, and coil

Here is what the caution above was about. With rotors. The United is larger and only works with their cap. It will destroy a normal cap. And if you put the United cap and smaller rotors from others the spark has to jump to contacts on cap
The United Cap shares the later models rotor so they can just make one.
That is what I assume. Lots of p places sell these including online Amazon and Rockauto to name just two. They are fine if used as a set together