december 2005 collectible automobile
according to an article in the above magazine, the 65 and 66s are interchangable. 67 had a new body design. also the 66 star chief executive is on a 124 inch wheelbase, same as the bonneville. the catalina and grand prix however are on a 121 inch w/b. whether that makes a difference in body panels i don't know.
it also only lists variations of the 389 and 421 v-8'* as options. i'm guessing if it has a 400 cube the motor has been switched with one from a later date.
also lists 45,212 executives as built in 66.
hope that helps