Brent, it will probably be a combo of headers with a cutout, for times like Drag Week, and open headers for times like the FER&R. Either way, it'll be free flowing enough to take advantage of the combo.
Chris, thanks for that diagram. That's a big help and saves me a bunch of research.
Ken, if I remember correctly, some of the combos I've seen that were optimized for the use of a full pump system will generate as much as 15-20+ HP. I haven't gone back to look at Jay's dyno experiment, but I believe it was in the 20 HP range. I realize it's not exactly apples to apples, but if Brent and Barry can see a 5-8 horsepower or torque gain on a somewhat milder engine, I'd think that's a fair enough comparison to assume that, while it's certainly not as good as a full pump system, it does generate at least a 1/4 or more percentage of that. Maybe even up to half as much on comparable engine builds. Of course the header evac system is only functional at higher RPMs, but I'm not talking about low RPM use anyway.
Thanks to everyone for your replies.