True story:
What happened was that in '64, the 426 Hemi came out and kicked everybody's butt badly at Daytona. Only thing was that the Hemi wasn't offered in a production car, it was strictly an over the counter deal for selected teams. Ford lobbied NASCAR to allow them to run the cammer. Nascar said "No way!". Things got so heated politically (Ford threatened to withdraw factory support)and finally NASCAR, banned the Hemi and the 427 high Riser heads and stated that any motor used in competition had to be
installed in at least 500 cars available to the general public for the '65 season. Chrysler withdrew and Ford developed the 427 Medium Riser, won just about everything in sight including the '65 Daytona 500. NASCAR let the Hemi come back towards the end of the season, Ford started politicing for the cammer again, NASCAR still said "no" so Ford withdrew for most of the '66 season, coming back at the end of the year when NASCAR allowed them to use the smaller Fairlane body.
Roughly 200 of these engines were produced, around 50 as dealer add-on cars (i.e. like MR norm hemi's, or yenko's) bought from the public. Meaning there was not "option" for the engine, back then you could buy a car without the motor and pruchase a cammer out of the catolog and the dealer would install it. But the majority went strictly for drag racing use.