Although I have never dealt with a built motor I will say that something that needs to be as exact as a high powered turbocharged engine having a shop do it is best. Who better to eat the $5000 bill for messing up other then a shop. If it fails and is due to their mistake they will end up paying for it. If you do it yourself and it fails your SOL. Butler and Mac Master is really looking for a way to not have to pay for it. Pistons out of tolerance would fall on the piston manufacturer, valve failure would fall on the valve manufacturer. And so on. As far as being a small block chevy shop, like others have said, they do more then that. My high school used them for a few of the automotive projects that went on.