In 1964 beginning with the first 426 production Race Hemi Dodges and Plymouths, single exhaust was installed to take weight off the car. The cars were equipped with very special four piece headers, two pieces per side that came back to lake type cut outs very similar to Max Wedges. The single exhaust started out as a "Y" pipe that hooked up to the lakes and went back as pipe only to the rear bumper where the muffler was mounted behind the gas tank, parallel with and just ahead of the rear bumper. The single exhaust was very restrictive but met factory installed exhaust system requirements mandated by NHRA so the racers only had to uncap the lakes forward of the "Y" pipe to greatly improve flow far superior to any regular full dual exhaust system. Everything I have found so far in original 1964 magazine articles, cars I have been fortunate enough to see in person and people much more knowledgeable than myself suggests this was the standard on the 330 and Savoy aluminum front end sedan models with 426 Race Hemi.
In mid June, 35 steel front end hardtop Dodge 440s and 35 steel front end Plymouth Belvederes were built with 426 Race Hemi engines. These cars were equipped with dual exhaust instead of the single exhaust like the sedan cars had. This Dual system also used the special four piece headers but switch at the lakes to a more production type dual exhaust system with dual mufflers mounted in the standard production location. The intermediate piped from the lakes to the mufflers are the same as a Max Wedge as are the mufflers but the original NOS tail pipes I have seen were aluminum. I don't know why just the tail pipes but that's what I have been able to find so far.