In my opinion ,the money that it takes to make a set of factory heads decent ,you can buy aftermarket for the same or a little more.I use Iron Eagles a lot ,I can get them really reasonable from a local Dirt Track dealer and I have never had any problems with them.
If you take a set of stock GMs Hot tank and surface them ,install guides , three angle valve job, springs and retainers , maybe replace some valves. Well around here that usually means a shop bill in the $600 range.
Like I said just my opinion, I could be wrong.