I'd custom fit the nocks with dental floss. When you get the size you want, soak the floss with super glue and it should last as long as the string.

BC nocks are my favorite. There's little if any difference in the throat size between 11/32 and 5/16.

I take old nocks off with a sharp knife and pliers, but you can screw up an arrow if you aren't careful.

Chad