Hi, This is taken from my 1963 Ford shop manual which also has 63 Mercury codes which could vary slightly from 64 codes. So herewith best I can do for you unless someone has a 64 Ford-Merc shop manual.
5BB...I don't know what the 5 stands for but the BB is paint code which is one solid color..Black
345 is a interior trim & upholstry code...my numbers for the Merc info only go up to 341
JB = 390 cu.in. with auto trans.
163C, 1 indicates its a V-8, 63C is the body style which is a two door hardtop fastback model.
64L.....64 is the year and the L indicates its left hand drive. 072721....thats the consecutive unit number off the assembly line.
These are for Canadian Codes. U.S. codes are very different.
You could also try getting some info from the
galaxie club of Canada. The Galaxie Club of Canada