Action Plus vs ......... any gains?

That's probably enough of a difference to get you into the 13s I bet. Where is your initial timing?
the tuning your talk'n about may get me into the 13's. Perhaps. There may be something left in the tune, but I'm a tweaker :D I believe it's at 16* initial, and 36* full. I've tried adding and pulling out, but this is where it ran the best. Probably some jetting games to be played with the carb.