Toxicbugman, I think you got the month codes wrong, Y can never be december and G can never be july. Y in 1964 is october and G in1966 is december.
In the aussie built cars the year and month letters have changed place compared to UK built cars, but they are coded the same all over the world.
suebutcher, you write "month and year" but I think you meen year and month.
my -63 GT has Z77C533288E, Z saying Dagenham UK, 77 2 door GT, 5 designated for export market 33288 serial and E for april. My 1966 estate has BA87FU62140 B Uk, A Dagenham, 87 estate F 1966 U june 62140 serial
change between the two configurations was made january 1965.
Power is how hard you hit the wall, torque is how far you move it.