In my OS engines I run OS plugs and I run HPI, McCoy or RB in all my others and I do not have a problem starting any of my engines even my .28 (K4.6) in my Savage with a pull starter with over 7 gallons run through it. Keep in mind changing the heat range of a plug changes the ignition timing. Safest thing to do if you are not sure is to run what the manufacture recommends or at least the heat range they recommend.

If you know what you are doing you can increase performance some by what heat range plug you run but you all so can mess up and engine if you do not know what you are doing.