90% of the Honda blocks are open deck. And them being JDM or USDM doesn't make a difference, they're structurally the same. For boost applications having a closed deck can save you in a cinch. However these days in the hands of a good tuner, there have been stock open deck blocks withstanding high amounts of boost. For example, one of Full-Race's drag Civics utilized a stock sleeved open deck D16 and made around 729hp. Reason why it didn't pop? Good tuning. Don't fall for the common myth just because it's an open deck it'll be weak.