That "R" signifies a "resister plug". The base manual for the GEN I bikes recommends the DPR8EA. 2010 bikes spec the NGK, DPR 8EA/9 plug.
Using the stock resister cap, you can run the non-resister plug. If the cap has been converted to a solid core, use the resister plug.
You may experience static in your AM radio in the absence of spark plug resisters. It may also put you in the cross hairs of people who own rifle scopes AND watch TV off of antennas.
many a trip continues long after movement in time and space have ceased- Steinbeck, [I]"Travels with Charlie"
[FONT="Century Gothic"][I]Sometimes your only available transportation is a leap of faith[/I] [/FONT]