[Zoomad75]

Here's what you need your machine shop to do to the Vortec's while they have them. First, have them enlarge the spring pockets for standard size small block springs. L31 springs are a smaller than normal diameter and will be a limiting factor to a larger than stock cam.

Second, have them machine down the valve guide bosses. The L31 valve guide bosses are the problem with higher lift cams as they are tall enough at max lift the spring retainer into contact with the guide. That's not a good thing at 5,000 rpm.

Those are the main two items to get done. Yes you don't have to do them if you are running a small cam, but it's easier to do now and know you can move to a larger cam later without having to pull the heads again.