As Jim mentioned: The 731 code you mentioned is listed as a "dual stage" H.D. air cleaner. The air filter itself is dual stage.

The firebirds all had the singe snorkle, at least the ones I know to be documented and correct... I've seen many with the dual snorkle air cleaners on them, but none were documented, and most also thought it could have been easily changed along the way as most figured the dual snorkle would provide more air...

But all the documented info I've seen to date indicate that Firebirds had the two (three if you count late 67 production as they possibly changed to the 68 version etc) While the 68/69 had the single with the two lid options (Black or chrome)

Was searching for some info for the filter elements and saw this topic again... sorr to bring up old posts..

Brett - 67 Drop Top 455!