If I were to replace the stock valves with manley street-flo valves(undercut stems) would I have to get a valve job? The heads are vortec's(brand new out of the box). Think it will help the flow in the vortec's or not worth the money?

 

Yea, it will help with airflow, just like any other head.

As for machining for the new valves, probably not if they are going to be the same size valves. I'm not positive if GM is using a different valve face angle on those heads, but I doubt it. Don L if he is around would know.