Lemmie tell yall a little story regarding this very thing. Back in early '99, RIGHT after my work accident, I couldn't do anything. Some days I couldn't get outta the bed. Hell......every once in a while I still cant. Anyway, at the time, I had just pulled the 318 outta my '73 Dodge club cab to do a 360 swap. I had to end up letting a local machine shop in Macon handle the job. I hired them to assemble it and one of their employees to install it on the side at his home. Found out I had a car oil pan so I ordered a truck pan from Summit. They sent the wrong one. unfortunately, I could not return it, because said idiots at the machine shop had tried to "modify" to fit the pickup that has also been sent for whatever the pan application was for. They butchered the pan up so bad, I could not return it. Fast forward to the "completion" of the "job". I got my truck back and all seemed to be well. Until one day the wife came home with a lot of valvetrain noise goin on. So, frustrated, at this point, I MADE myself climb into the engine bay and remove the valve covers. Yup, just as I suspected. The rocker shafts were installed upside down and backwards. This from a machine shop with more than FIFTY years experience in the Macon area. I also noticed that they guy who installed my engine crossthreaded all but ONE header bolt. Yeah. I'm tellin yall, those of you who don't know how to do this yourself, LEARN and learn to do it RIGHT. It will serve you well in life.