Would it even be worth my time (and money) to replace the stock valves in the Vortec heads with aftermarket valves? Undercut, or swirl polished...something like that.

 

lot depents on how much jack you have to drop and how you define worth it. if i were going to do it i'd buy manely valves with the reduced stem and swirl polish. you get a better valve and more flow. you can also go with a 3 or 5 angle valve job, or just undercut the back side of the valve 30*. you'd want ported heads and all the other tricks if you do this i'd think or you wouldn't realize all the gains you could have.

 

Then again, if you wanted to increase the valve face size, you'd have to get different valves. Like Ed says, the Manley Race-Flos are a good valve at a good price. Typically the larger diameter valves weigh less than the smaller stock valves, so you get the advantage of a lighter valve train as well.

 

If it'll flow better with a reduced stem and a swirl polished face then it's worth it to me.

I don't want to take the heads off once I get 'em on so I want to do all this now.