I have a 67 Firebird and just got my PHS paperwork back and have a question. I always thought I had the standard 400 4bbl engine. Apparently, my car came with the 400 "A.I.R." (code WU)engine. The sheet shows that only 1220 were built in 67. What exactly does the "A.I.R." mean and where can I verify on the engine that I actually do have this rare engine? Thanks!