I did some research on the Internet Hockey Database. I looked at the season of 1960-61. I am currious to know if there were working agreements between NHL and AHL clubs as there is today. It would be interesting to hear what your cousin has to say about the contract system at the time A Lone Wolf.
Where NHL Clubs Got Minor-League Players in the 1960-61 Season
Boston Bruins - Providence Reds and various EPHL
Chicago Blackhawks - Buffalo Bison
Detroit Red Wings - Hershey Bears
Montreal Canadiens - various EPHL, esp. Hull-Ottawa Canadiens and Montreal Royals
New York Rangers - Springfield Indians
Toronto Maple Leafs - Rochester Americans
Other AHL teams: Quebec Aces - One player from 1960-61, Jim Morrison, also played with the New York Rangers during that season. He would play the following seven seasons for the Quebec Aces, plus one more in the AHL with the Baltimore Clippers, before returning to the NHL with the Pittsburgh Penguins. Cleveland Barons - Not one Barons player played in the NHL during the 1960-61 season.
Easern Professional Hockey League notes:
Montreal had a few players that played for Hull-Ottawa of the EPHL. Two or three players also spent some time with the Montreal Royals of the EPHL, including the great Jacque Plante.
The Bruins also had players that were member of various Easern Professional Hockey League teams, especially the Kingston Frontenacs. This includes the legendary Willie O'Ree, the first black to play in the NHL. O'Ree played for Hull-Ottawa for part of the 1960-61 season before his rights were traded to the Montreal Canadiens in the offseason. O'Ree played part of 1961-62 with Hull-Ottawa before being traded by the Canadiens to the Los-Angeles Blades of the Western Hockey League.
As far as I know, the Toronto Maple Leafs owned the Rochester Americans, and did so right through the 1960s until they sold the team during the Ballard years. NHL teams owned a lot of minor league teams as well as junior teams, stocking them with underage players they owned.