GS-R header would probably be the shortest of all (at least OBD I GS-R header) the O2 sensor is in the beginning of the cat and the header flange is much closer to the front of the car. Just get a muffler shop to make you an extension pipe, cost me about $25 and never had a problem.
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Andy - Reinstated
Hybrid Forum Moderator
'06 Subaru Legacy Spec B - Stock, for now
'98 Civic EX - CTR headlights and grill, Kosei K1's, for sale
'90 240SX - SR20DET that will never get installed, project car.