The cast iron Sanderson headers I use are PN QP1000S that have 2.5"
center outlets and have anti-reversion dams cast in. True tube headers will
probably make 10-15 HP more at peak RPM but the cast units are very quiet
for daily use. I did spend the extra money for thermal barrier coating and
it is worth the investment whether Sanderson or Powercoat does it. My down
pipes are hand fabricated out of 2.25" pipe with a Flowmaster collector
leading to the 2.5" highflow converter. 
The Sanderson company at 517 Railroad Ave, South San Francisco, California,
650 583 6617

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jones.775@osu.edu  Andy Jones  Feb 2001