There is a big difference between a Mechanic and a machinist.My machinist was a perfectionist.Ive turned wrenches as a pro for over 30 years.I still brought my stuff to him to do.Lots of stuff Id check but with a good shop Its cheap insurance.Yeah a lot of people jus buy and bolt on.Some get away with it some dont.My buddy bought a hi buck set of heads for his Camaro.Didnt check them and in less than 100 miles had lots of problems.Between bent push rods and having to replace guides he had a lot more than having a shop check them.Rocky