Its way more important that you get the correct size headers than a truly tuned exhaust system.With the correct headers you will get the same increase of power as using the correct intake,perhaps more.as most race cars make more power with open exhaust the easiest thing for a person to do is put the least restrictive system on after the headers as money allows.You can go into pages and pages as to shape/length of pipe after the headers round Vs oval.reducers for velocity,tapered expansion exits and a lot of other things that make a slight difference at a high cost. What old said is true and complicated.
for your application I think the old smaller heads with dual plane intake and 1 5/8 headers will make it easier to tune.If you want the bigger heads then consider what old said about adding a pressurized intake system.If you want normally aspirated and only race high altitude(you didnt say how high?) then more CR would help and a higher RPM cam to take advantage of the bigger heads and intake.Your 1 7/8 headers are way too big. I use 1 7/8 headers on a 434 with 10.75:1 with a 256/264 duration solid roller cam ,its lift is .420X1.6/1.5