[3] Kellett played fullback and scored a goal in Hull Kingston Rovers' 5-13 defeat by Widnes in the 1963–64 Challenge Cup Final during the 1963–64 season at Wembley Stadium, London on Saturday 9 May 1964, in front of a crowd of 84,488, and played fullback, and scored a record eight goals (from eight attempts) in a Challenge Cup final in Featherstone Rovers' 33-14 victory over Bradford Northern in the 1973 Challenge Cup Final during the 1972–73 season at Wembley Stadium, London on Saturday 12 May 1973, in front of a crowd of 72,395.

Kellett played fullback, and scored a goal in Hull Kingston Rovers' 2-12 defeat by Hunslet in the 1962 Yorkshire Cup Final during the 1962–63 season at Headingley, Leeds on Saturday 27 October 1962, played fullback, and was man of the match winning the White Rose Trophy in the 25-12 victory over Featherstone Rovers in the 1966 Yorkshire Cup Final during the 1966–67 season at Headingley, Leeds on Saturday 15 October 1966, played fullback, and scored a goal in the 8-7 victory over Hull F.C.

in the 1967 Yorkshire Cup Final during the 1967–68 season at Headingley, Leeds on Saturday 14 October 1967, played fullback, and scored three goals in Featherstone Rovers' 9-12 defeat by Hull F.C.

Kellett played in Featherstone Rovers' 0-4 defeat by Warrington in the Captain Morgan Trophy Final during the 1973-74 season at The Willows, Salford on Saturday 26 January 1974.

As of 2013, he is third on British rugby league's "most goals in a career" record list behind Neil Fox and Jim Sullivan, and as of 2015, with 3686 points; and is seventh on British rugby league's "most points in a career" record list behind Neil Fox, Jim Sullivan, Kevin Sinfield, Gus Risman, John Woods and Mick Nanyn.