It's a mystery why OS plugs like the #8 have such short threads. There are ample threads in the head for a true long reach plug. In theory a hot plug like the F will advance the combustion timing slightly and/or require a slightly richer needle setting to offset that. If you are having flameouts though due to the plug getting wet with an inverted mounting position, the F plug makes more sense than using an idle bar plug which will cost you a few hundred rpm on the top end.

Ernie