Bolt them together (with stove gasket in between) and put a straight edge on there and see how they look. If they are pretty far out of whack then you'll probably want to resurface them. If there are just a few highs and lows here and there, you can probably get by using a long sanding board and a couple hours of sanding. Be sure to get Remflex gaskets as well. You don't want to spring an exhaust or vacuum leak and go through the whole process again down the road.
