The first hp 273's either had no muffler or a straight through muffler. Apparently the combination was too loud and they used a low restriction Hemi style muffler. It had a distinctive sound because it was a single system. The original system from what I have read was a scavenging designed crossover pipe with a 2 1/2" intermediate pipe into a low restriction Hemi style muffler and a 2 1/4" tail pipe into a bright tipped resonator. I have heard some of the early resonators weren't chrome but just painted. I think some NOS pieces have been found. Accurate LTD makes a nice replacement system for these cars.
The early systems had a 2 1/2 straight through muffler, followed by the 2 1/4 straight thru resonator. It is a nice alternative to duals if you lack space or want to simplify your system.
