Dasher - what a superb trivia question and I apologize I haven't been on due to an increased workload at the office as well as working tirelessly into the night to convert my Giant library to DVD.
Off the top of my head, I would have guessed that guys like Frank Gifford and Joe Morrison would technically qualify since, despite the fact they were primarily RBs for the majority of their respective careers, they were both switched to WR in their later years with the club (i.e. Gifford in 1962-63 and Morrison I believe in 1967 or 1968).

Again, me with my "technicalities" ... maybe Grizz was right in that I should have been a two-bit lawyer versus an engineer ... ;D
Peace!