How rare is a cassette player/mic option

[1966 dart wagon]

Alright from what I've found so far its in a package called A78 which included a bunch of stuff:

Afew options: A78 - Formal Roof which includes the C26 overhead Console, small back window and vinyl top; power windows, 6way leather seats, rallye gauges, belt molding, stone shield molding, rocker molding, pedal dress up, International export (Made in USA tag), Cassette Player w/stereo speaker, rear defrost.....

taken from:
http://www.forebodiesonly.com/forum/showthread.php?t=214&highlight=cassette+player

Anyways My dad has had this for quite some time, its in pristen condition and he does have the mic, we were talking tonight about it and he was wondering how rare this is, we are assuming it is since he has never seen one before.

Thanks for the input, I promise to get pics, little to late tonight though.

-Jack