Ok I wasnt sure if what you meant. If you dont want duals order

http://www.summitracing.com/parts/wlk-40491/overview/make/dodge/model/d350/year/1984
run 2.5" back and through the muffler to this(modifications may be needed for this ie cutting it shorter)

http://www.summitracing.com/parts/wlk-45105

Doing this to my 75 rite now