You better check the rules for ARA factory class before you start spending your money. Technically, taking a barreled action and dropping it into a factory stock is violating the rules. You're building a rifle, so by definition, that rifle isn't factory.
Having said that, take your barreled action and put it in a factory stock, and keep your mouth shut about what you did. I'm not the ARA police.
Accuracy? Buy all you can of the lot # of ammo that your rifle shoots the best and spend hours learning how to read the wind.
I've been shooting ARA factory class for a few years and I'm really enjoying it.