Good Question With the expansion of the Super Stock Division in the NHRA in 1967, each manufacturer was out be the 'Top Dog'for 1968. Chevrolet was supposed to put together a 1968 Corvette Super/Stock car with an All-Aluminum 427 rated at560 Horsepower. Installed in the 1968 Corvette with an approximate weight of #3100 lbs. The Corvette would have had a Weight/HPfactor of 5.53 Wt/HP putting it in the new SS/A Class for 1968. Ford was in the process of putting together a 427 SOHC in the new 1968 Mustang GT. The 427 SOHC was to berated at 600 HP. Installed in the 1968 Mustang GT with an approximate weight of #3200 lbs. The Mustang GT would have hada Weight/HP of 5.33 Wt/HP putting it also in SS/A. Mopar, to counter Chevrolet and Ford's effort, went with the 426 Race Hemi in the light A-Body {Barracuda and Dart}.The Race Hemi would again be rated at 500 HP, just like the 1964 and 1965 Super/Stock B-Body cars. The #3050 lb. lightened A-Body cars would have a Weight/HP factor of 6.10 Wt/HP. These cars would be classed in the 6.00 to 6.99 Weight/HP range, or SS/B. The Head's of Mopar's Racing Division {Dick Maxwell, Bob Cahill and Tom Hoover} had Engineer - Bob Tarroli designthe project in November 1967. This is where the 'main ingredients' started.