Ok, my factory manual doesnt mention the L except for late models. It also says the plug should have a 12mm reach, the L has something like 20mm reach (from washer to electrode).
Thats why i wondered, the factory manual suggests short for anything up to about 75/76, long for late k series, but doesnt specify which for a F.
Just thought, the R means its resisted right?
I have electronic ignition with 5000 ohm caps, does that make any difference?