Update to the snippet Jeff posted above:
The "Ram Air' option for the Formula was indeed offered right up until the end of the 1974 model year. It is documented in the GM parts manual, although it's pretty confusing and hard to interpret. You could order -- from the factory -- a Formula with a non-SD engine AND working hood scoops. A poster over on TAC finally wallked me through it step-by-step, and he was right.
However, you could not get that combination with an SD engine, and you could not get the functional shaker on a TA after the end of the 1972 model year. Pontiac paid for the R&D on the SD engine but would not certify it for the EPA with the working Formula hood. They either could not or chose not to do so for the TA, hence the might SD engine was hampered by the stock restrictive intake system. I think it shows how close Pontiac was to following the suit of all other car makers and giving up on performance, since the certification process had to be cheaper than the R&D effort on the SD engine. I believe that the higher-ups at GM decided that they would never sell enough SD engines to recoup their investment and decided to call it quits before they sank any more money into the effort, and just ran with the SD engine until the EPA certification done for the 73 model year needed to be redone (in 1975). They switched to the catalytic converter technology in 1975 (thus requiring the single exhaust converter) and that's when any serious engine work stopped. The "HO" engine released in the spring of 1975 was 4 speed only and basically just a station wagon engine (no HO parts in it). GM did not certify the 455 in the F-body with an automatic transmission, and when the emission regs changed again (for the 1977 model year) they dropped the 455 altogether in the F-body.
