The Mk IV version was manufactured for the 1964 and 1965 models years, but you'll find some with 1963 serial numbers, as manufacturing of the 1964 models would have commenced in late 1963, to build up inventory and have the new model in stores for the lucrative Christams season.
1967 serial numbers could be either an Imperial 700 (1966 & 1967 model years) or an Imperial GT (1968 & 1969 model years) that was manufactured in late 1967.
The Mk IV version was manufactured for the 1964 and 1965 models years, but you'll find some with 1963 serial numbers, as manufacturing of the 1964 models would have commenced in late 1963, to build up inventory and have the new model in stores for the lucrative Christams season.
1967 serial numbers could be either an Imperial 700 (1966 & 1967 model years) or an Imperial GT (1968 & 1969 model years) that was manufactured in late 1967.