Don ... your idea with the floating Rapala is fine, and should work OK. As big as a Crappie's mouth is, even if the fish isn't much longer than the Rapala, that fish will try and grab a bait of that size. I know, because I've caught some Crappie no bigger than my hand on 300 series Bandit crankbaits
Now, about using the baitcast reel (level wind) to cast jigs lighter than 1/4oz ... that's a problem. But, with added weight or a float, that might be doable ... but you'd just have to experiment with that idea, just to see how light a rig you CAN cast for any distance. You'd probably be better off to go and buy a inexpensive spinning rod/reel combo for light lure casting. Your 6# test mono will work fine on most any med sized spinning reel, but if you go Ultra-lite size on your reel, then you would definitely be better off with 4# test.