Steve: I can't answer your question as far as length/action/weight are concerned but I do know that it can be done as I fished that way years ago when I wanted to only pack one rod into the Uinta Mountains. I used mono line (6 lb?) and attached a egg shaped bubble on the line, then a swivel, then a 4 lb leader to the fly. I filled the bubble with water for weight and let her fly. It was about the only way to fish some lakes because of the numerous trees surrounding the shore. The biggest drawback as I remember (this was 50 years ago) was that the reel was seated too far back to make casting and reeling enjoyable. With the advent of these light weight graphite spinning rods I have no reason to attach a spinning reel to a fly rod except in an emergency.

Tim Anderson