One other thing I remember about muscle car era end is that the low compression and Net HP ratings turned the die hards away from new cars. They really thought the net HP #'s were same measurement as Gross HP.
Also, new car prices were starting to climb in 70's, so many turned to the abundant used car market which had cheap late 60's cars. My uncle was in teens then and called anything after 1970 as a 'plastic fantastic'. Had a 69 Z-28, then turned to Datsuns.
Anyway, the SD motor was developed before there was any throught of gas lines, and the 'colonnade' A body was meant for 1972. Imagine if the 1972 GTO would have had a Grand Am front end? or LeMans with no 5 MPH bumpers?
