Blueprinting as mentioned is attention to detail to an extreme. It is also limited only by imagination. As Jerry said, a good common sense build with extra time and attention.
Years back, I read an article on building a drag race super stock engine. The super stock was essentially building an engine to the max using stock specification parts whose only real improvement relates to durability. One of the steps that stuck in my mind was after checking clearances, ring end gaps, etc. He loaded the pistons with rings and pulled them through their bore with a weight scale to make sure they all had the exact same drag. He may have to switch rings around until he got the exact same pull. If you think about it, it makes good sense but I myself would never have thought about that. Seeing the amount of horsepower gained with just those types of modifications was un-real. On a six cylinder, the power is probably not the goal but the reliability and longevity of such a rebuild could be.
