Mysterious fin unit...
 

Several years back I picked up a couple of these fin units in a hobby shop junk bin; I used one to scratch build an 18 mm rocket I call the Wind Raider. The rings fit a tube with an O.D. of 30 mm - root chord is 2.5", span is 2" and the tip is 1.125" in length. I suspect they were manufactured for an old MPC or MRI rocket, but I can't identify it.

Can anyone shed some light here?

Yes, those were used on a few Quest rockets. They fit the T-30 tube as I recall.

The name "Apollo" comes to mind. A fake-scale model with a transition unit.

MPC/AVI (and later, Quest) made these units available. At least the rings. The MPC/AVI fins were shaped like those on the Redstone. I don't remember a MPC kit that had the simpler planform, but the set you have there goes on the Quest Apollo (http://www.ninfinger.org/rockets/no...a/92qst12.html). I still have mine, but all the fins are gone.