McKinstry played in the Canadian Football League with the Montreal Alouettes and Ottawa Rough Riders from 1961. While playing on the Grand Rapids Blazers in the United Football League (1962), McKinstry was recruited by the New York Jets as a free agent. He also had interest from other teams, such as the New York Giants. McKinstry played as a tight end with the Jets from 1963 to 1965.
During his time with the Jets, McKinstry worked full-time on the off season for Grumman Aerospace Corporation in Bethpage on the project management team. He coordinated activities for the Lunar Excursion Module (L.E.M.) and was the Night Director for F-14 Tomcat production. McKinstry worked on the proposal plan for the X-29, which was placed in the Smithsonian Air and Space Museum.
During his time at Grumman, McKinstry's love of education grew. He obtained a Bachelor of Science Degree in health and physical education at LIU Post in 1976. After completing a Masters of Science Degree in education, special education and adapted physical education at LIU Post in 1978, he was appointed to a faculty position in Health, Physical Education, and Recreation.
Expanding on his graduate thesis in speed development, McKinstry launched his own business, Nu Tek Athletic Consulting Ltd, in 1986. Nu Tek Athletic Consulting Ltd specialized in speed training for professional, college, and high school athletes. McKinstry lectured at various institutions such as LIU Post, Yale, and the Joe Namath Football Camp.
In 1994, McKinstry began working for the New York City Department of Education. During his four years he was an adapted physical education tenured teacher. He also taught special education to SIE VII students.
McKinstry worked at St. John's University as an administrator from 1998 to 2014.
McKinstry now volunteers at various organizations, such as the Sunshine Foundation and Intrepid Sea, Air & Space Museum, teaching young children about the benefits of education while perusing their interest in sports. He also supports head injury awareness, speaking at the Head Injury Association Sports Forum.
His son, also called James, was a scholarship tennis player at St. John's University as well as walk on football player. His daughter Kelly was a scholarship basketball player at Molloy College and his other daughter, Erin, was a scholarship tennis player at Fordham University.Two-year junior college first team all-American in American football - Farmingdale State College (1960–1962)
Full academic undergraduate scholarship to LIU Post (1970–1976)
Featured in Life magazine pullout with the New York Jets (October 25, 1963)
Joe Namath Football Camp lecturer on speed development
Industrial League Basketball Coach of the Year (1979 and 1980)
Sports Hall of Fame - Farmingdale State College (1995)