I'm looking forward to what you come up with, Tim. The best I can recall from what I know about small block Chevy engines:
-Decreasing tube diameter increases low-rpm exhaust speed, which in turn helps low-end torque through more efficient cylinder scavenging. This *may* lower upper rpm power, but how bad could it be on a 1.0?
-Longtubes are better than shorty or block hugger headers for low-rpm situations (towing, economy).
-Thicker material and/or header wrap will keep heat inside the collector tubes, keeping exhaust speed up for better scavenging. This is for all rpms.
-Port match!
All dyno test I have seen are at WOT. Since we rarely go past 1/2 - 2/3 throttle for short periods and spend a lot of time at part-throttle, this seems to indicate smaller tubes than usual? I think you could go down to ~1" on the collector tubes, since each cylinder is only 0.33 liters of displacement, versus 0.713 liters/cylinder on a 350 SBC.