The Doug's headers on the D/Darts are slightly different then today's headers. They had 1 3/4" primaries with 3" collectors. Today's are 1 5/8" with 2 1/2" collectors. They had a special built 2 1/2" y-pipe that mounted to the header collector. It necked down to 2 1/4" before the muffler. I believe they had both a muffler and resonator since they ran in D/Stock.