Back in late 1956, I was heavy into
Chrysler high performance cars. To the best of my knowledge the D-501
convertibles were produced in very very limited numbers and were made to
compete in the convertible races that were popular back then.
They came in one color, white, and they were all stick shift, there
were no automatics made for racing.
As far as some of the hardtops coming with dual quads and cam
in the trunk, well, back then if you had the right dealer with
factory contacts and a little money you could get some pretty wild
stuff from Chrysler's assembly lines.
Ron