Usually, you can get by just with doing the #1 cylinder. The valves in the head for that cylinder are generally the shallowest when prepped for racing, so you know if those have adequate clearance, then the rest should be ok. So, the next question is are the valve seat depths in the cylinder head consistant, or do they vary a whole lot. If they vary a lot, you might need to loosely assemble the engine, and clay the tops of all the pistons to see if any are closer than others to eliminate that one that seems to always come back and bite you because you assumed or overlooked it.
