apparently
a 1965 NZ 3d is 16.3mm
a 1965 HK 5c is 16.5mm
a 1961 Malaya 5c is 16mm
so if this is accurate then technically I'd think it should be possible to determine which of the 2 it is (assuming you had the actual NZ muled coin and the equipment necessary to make exact and precise measurements). Although the dates should be enough of a giveaway, really.
a 1965 NZ 3d is 16.3mm
a 1965 HK 5c is 16.5mm
a 1961 Malaya 5c is 16mm
so if this is accurate then technically I'd think it should be possible to determine which of the 2 it is (assuming you had the actual NZ muled coin and the equipment necessary to make exact and precise measurements). Although the dates should be enough of a giveaway, really.