I started racing NHRA stock in 1973 when you had to have the complete exhaust system on with either cut outs or disconnect from the mufflers.
The next year we where allow headers with the exhaust system still on.
A guy named Dave Benesick (SP?) had won the NHRA stock World championship from 1970 to 1972 in a Buick stage one, this was when you won World championship by winning the World finals, no points involved like today.
I think the best it ran was around 11.80s on soft bias ply street tires like M&H still makes today
I bought my 1963 Plymouth Belvedere 415 HP M.W. 2 door sedan in 1973 and started racing it with the original exhaust system on it with the cut outs open at the old Irwindale 1/4 mile drag strip, it ran 12.60s missing a little with the stock converter, changing the converter to a good 8 inch race converter made that car pickup over .7 ET and almost no loss of MPH
My first race I won at Mickey Thompson old Fontana Drag City in Fontana, CA ran 17.6 or so in K/SA formula 3, it was my mothers new 1964 Dodge dart 270 4 door with a 273 C.I. two barrel motor, whup up on all the Chevy and Buicks in the same class
I've been hook on drag racing ever since