What is the correct NGK sparkplug
 

What is the correct NGK sparkplug for an 1988 3.2 L?
Bpr6es or Bp6es
Whats the difference between these two?

The r is for resistance. I don't think they make the non resistance plugs anymore. I use NGK bpr7es in my 88 3.2. They work just fine.

The r in the designation means there is a resistor built into the sparkplug. 911s usually have resistor sparkplug connectors and possibly also resistive sparkplug wires. Technically this should cover the resistance needs for RF suppression without also requiring resistor plugs. It's worth confirming this by measuring the resistance of your wires, as they've most likely been replaced at some point.

I've not owned a 3.2, however, so hopefully some owners will chime in with direct experience.

Stock ignition wires (Beru) do include a resistance. Since they vary in length so does the resistance. I use Magnecor 85 and I think the resistance is in the plug connector, not in the wire, so all six wires show the same resistance.

Stock distributor rotor also includes a 1kohm resistor.