That year, when he was 17, still shines brightly in his memory, as a time when several life-changing things happened.
The first was his decision to leave his home and school in Ohio and undertake upper sixth form studies - now year 13 - on the far side of the Pacific, at Otago Boys' High School, as an AFS scholar.
AFS is a not-for-profit organisation that aims to create a ''more just and peaceful world through intercultural understanding'', and overseas student exchanges.
Among Mr Porter's highlights of that year was attending a June concert by the Beatles at the Dunedin Town Hall.
And he still vividly recalls the vigorous dancing and the ''wild'' response from the youthful crowd as Beatlemania hit Dunedin.
Mr Porter spent that year with fellow OBHS pupils Neill Baker, also in the upper sixth, and his younger brother, Bruce, from his Dunedin host family, and the trio became close friends.
''They were my brothers,'' Mr Porter explains.
Mr Porter, accompanied by son Tim, is staying with Neill Baker this week.
It had been ''wonderful'' to see him and to visit their old Dunedin school together yesterday, Mr Porter said.
And Mr Baker welcomed the chance to see his American ''brother''.
''We've had a great catch-up together''.
Mr Porter's educational venture to Dunedin in 1964 was, at times, quite challenging.
He faced some culture shock, including initially confusion over unfamiliar New Zealand vocabulary, and colloquial terms like ''fair go''.
And some science subjects were different and demanding, but he appreciated the friendly and ''welcoming'' response from staff and fellow pupils.
After Mr Baker and Mr Porter parted at the end of 1964, their lives took different directions.
After gaining a University of Otago MA in geography, Mr Baker later worked at OBHS, both as a geography teacher and then as a careers officer, retiring in 2010.
After a long career as an optometrist, Mr Porter retired last year, and now lives in Georgia.
The two men have kept in touch over the years.
Late in 1964, Mr Porter walked the Milford Track, before returning to the US.
And before returning to Dunedin this week, he walked that track again, this time with his son Tim, noting some big changes, including more bridges and much better catering at the huts.
''It's good for your overall health and wellbeing to do that Milford Track every 50 years.
''I'm going to sign up for the walk in 2065,'' he added, with a smile.
