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Have you thought of making your own manifolds? Ive almost completed mine with nothing but a grinder, drill, welder, and lots of patience and spare time, but i know they're how i want them.. Really depends on your time, budget and commitment. Total cost of steam pipe and bends has been $140, plus a few flanges added it up to just over $200 to complet my manifold from heads to turbo.... Sorry i forgot, i cut up my extractors for the header flanges, so you would have to add the cost of flanges to that estimate...
Why not run the standard manifolds bolted backwards?