Looking for advice, BB headers vs. HP manifolds

My brother Denny of HDK has a 383 (formerly 6-cyl) Duster and used TTi headers by
changing the #7 tube only. Don't know why TTi doesn't just make them all this way.
For access these were made with the engine/trans/K-frame outside of the car. I believe
that he may have made a slight change of the cross shaft ball on the bell housing also.

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