The first prefix R stands for resistor. I found out many years ago that my 68 340 GTS didn't run as good with the resistor plugs as the standard N9-Y. Might be that is just me. But then again I ran around with stainless solid core plug wires-they wrecked havoc with people's TV reception before cable.
I didn't use the resister plugs either . But that would just be more confusing for some members. The non resister plugs also interfere with some of today's later ignitions and Stereos.