Stock or ported 823's?
 

Will a set of stock 823's get me to 600+ hp on a 408 stroker motor? What would be the high rpm range be of the heads with good supporting components like ss intake valves, .660 lift dual platinum BTR springs, comp spring 528-kit and rocker arms that can handle 7000ish rpm. Or should they be reworked to optimize the flow. Who has good power porting? Is cnc better than hand porting? Will these parts even work together? I bought a fire sale off of a guy for a 408 gen 3 block, lunati 4030 4" crank, Texas speed 6.125 lt h beams and Wisco k464x3 -3 forged pistons.

I've heard 2.0-2.2 HP per CFM flow of a head...so looking at the intake side, Yes.

BUT, also heard they're week on the exhaust side.... mine are as cast on a LQ4 bottom end and been 7500 a bunch of times. (.660 dual springs)

Probably better off not spending the $ on porting and use it instead to get a really good intake like a FAST 102, unless the heads need freshening anyways. The LS3 manifold is great, but probably come up short if the goal is 600hp. If porting, I prefer CNC. The texture of a CNC porting actually helps flow compared to a polished-smooth port and with CNC porting you're going to get very consistent port to port flow results.

As Doug G stated the intake/exhaust ratio is not ideal being about 70%. So you'll want a great flowing exhaust and have more cam duration on the exhaust side. For headers, go with at least 1 7/8", preferably 2" primary long tubes into a 3" x-pipe exhaust.

Porting 823's
 

The heads need to be gone through anyway, I like to get them ported. To whom would I trust to do this task? Texas speed, katech or Eric Weingartner just to name a few. Who are the cnc porters? I do have a 3" pypes x cross overs with the violator mufflers and will use long tube headers I can move air thru the exhaust.

Are you looking for 600 at the wheels or 600 at the flywheel? 600 at the wheels through an auto tranny is going to take a lot more than 600 flywheel.

Gromm Racing has CnC ported fully gone thru rectangular port LS3 heads for $1600 I believe with no core needed. They have done a bunch of work for me and Semir puts out a quality product. They are in San Jose, CA

Here is the flow chart for their LS7 and LS3 style heads.