There had been a big discussion here locally about that, (a local restorer, [so he likes to call himself], swore the dual was correct, but he was wrong) and when Dan was looking at a few Dual Snorkle ones on ebay I mentioned that to him, and he did more research on the subject, and came up with the same results.
Firebirds only had the single snorkle or the R/A pans etc... such as the 69 T/A or RA cars etc...