A couple of comments as your build is very, very close to mine
- The Victor, if unported, is leaving some power on the table, especially on a big inch motor
- I'd be surprised if those stage 2 heads flow anywhere near there. I had a very similar flow table from KC when I bought mine, sent them back for other reasons and more porting and the next chart was less, but on a local table was about 40 cfm lighter. This was 2006, and I can't say I know what KC does up there, but that was my experience.
So if you want a big jump, you may consider having someone else port them, it took us quite a bit of work to get in the 320s after I decided to have someone else to do them. Again this was 2006, I haven't had any KC Stage 2s in my hand since then, but it could be something to consider. Those are relatively big numbers for an Edelbrock head, maybe Joe or Brent can comment on what they have seen with KC Stage 2s more recently
I don't know any header builders, but I'd assume if you stick a screwdriver in the exhaust port and look at the overall direction the port travels, you'll see the direction the primary pipe needs to go, combine that with delaying the turn as long as you can for fitment.
If you want to get serious with size and length based on engine characteristics, look for a program called PipeMax, it's cheap and has a good reputation for taking advantage of exhaust pulses for additional cylinder fill with primary pipe sizing and length
I am not a big cutout fan, but if you want them, they can reduce backpressure, especially if your exhaust is marginal. That being said, put them well after the O2 sensor, I'd recommend 18 inches, just to be sure the EFI doesn't get any funky feedback and try to adjust it out
Overall I think you will really like the engine, should be very happy on the street