An AA muffler installation included the inlet pipe clamp, muffler with integrated inlet pipe and integrated or separate outlet pipe, and support brackets/adapters. While all AA muffler installations used unique bracket supports and/or adapters, the standard A-5230 A chassis muffler was used on the majority of AA131‘s.
Closed body types for the 131-1/2″ wheel base were fit with an AA-5230 muffler and a separate outlet pipe starting in April 1931. All of the AA157 installations used muffler AA-5230 and a separate outlet pipe. The AA-5230 muffler was the same as the A chassis muffler but had no outlet pipe. The AA112 Standrive chassis used muffler AA-5231 which had a unique integrated inlet pipe and no outlet pipe.
There were three muffler installation for the AA131, four muffler installations for the AA157, and one muffler installation for the AA112.
An article containing the eight AA muffler installation is provided in the link below. This article is a PDF file (fairly large and therefore may take some time to open).
Both the A-5230 and AA-5230 mufflers are available at Aries Limited