I swapped my Tremec out for an AOD for the same reason, plus when I add the blower, I won't have to worry about missing a gear. If you go the AOD route make sure you have it built with quality parts. I put an Art Carr AOD in mine and love it. I manually shift it so,it like a stick without the clutch.
Check my sig for my time in NA form,, I am still agthering parts for the blower to be installed....
As for the headers/ H-pipe you might have to swap thise if you go with the AOD, but not with the C4.....