I went home yesterday and checked the numbers for, ummm, the hundreth time. I was wrong (of course). You cast on [some number], plus 7 for the steek*, plus 2 for "balance". Once you've done the oh-so-fun corregated ribbing, you increase to 320+7+1=328. Not that 320 is any more divisible by 33 than 312 is.
*This set of 7 steek stitches is for the cardigan opening. Valerie is right, there will be another 2 sets for the arm holes, but those will be added later. I suspect the sleeves will be another brain bender, but I'd rather not think about that for now.