43, 44, and 45 denote the heat range. 43 is the "cold" plug intended for highway driving only. 45 is a "town" plug intended for short trips, and has a higher heat range to keep deposits burned off the plug tips. 44 is midrange. "the "R" prefix indicates "resistor", which makes little, if any difference in the real world. Back in the dark ages, "resistor" plugs were made to avoid changing from wire-core ignition leads to the more modern resistance wires, to avoid AM radio and broadcast TV reception interference. Running resistor plugs and resistance wires together does not present a problem, especially if some kind of ultra-high voltage coil is used.

Lots of "old mechanics' tales" are repeated for decades by people with no understanding of when, or why they originated. Most of them are utterly irrelevant when someone does a little research about why they came into being.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!