The best would be the old original Fentons that bolted to the intake manifold and provided heat to the intake manifold. It may not matter much if your truck is mothballed during the winter.
The long tube headers don't improve the breathing much on a daily driver and the siamesed exhaust ports for 2 - 3 and 4 - 5 don't lend themselves to tuned lengths. The reason that crossover pipes aren't as effective on a Chevy six as they are on a V8 is that the exhaust pulses are evenly spaced on each manifold on the six, but are not evenly spaced on the V8.
