The first implementation was done for the 7090 by McCarthy (hence CAR and
CDR --- Contents of Address Register and Contents of Decrement Register).
If you want to see a tiny implementation then look for the PDP-1
implementation done by L Peter Deutsch. There's a book chapter and then I
found this report:
http://s3data.computerhistory.org/pdp-1/DEC.pdp_1.1964.102650371.pdf