Feb 1963 - unprefixed number by the dynamo (Tore)
1963 - MGB number by the carbs (Ste Brown)
May 1965 - unprefixed number by the dynamo (George Wilder) ...
... and carbs
About October 1966 - unprefixed number, very front edge of the inner wing on the dynamo side (Colin Parkinson) ...
... and the MGB number, just in front of the radiator, carb side
March 1967 - unprefixed number, very front edge of the inner wing on the dynamo side (Dave O'Neill)
Australian 1963 - top-left body number by the carb-side hole for the pedals, bottom-right chassis number at the very front of the chassis rail on the carb side (Ian Buckley).
Australian October 1968/July 1969 - body number beside the hole for the pedals on the carb side (Denis) ...
... and in front of the radiator alternator side
More info on Australian CKD cars here.