Try a SIG Kadet LT20. I believe that is what they call it. Goldberg and Great Planes also make 20 size trainers. With the 25 you already have I would use the radio and motor out of the Cub. I would buy a kit because I don'y think you can get an ARF 25 size trainer. I do not do ARF's so I kinda glide past them. Hopefully someone here can point out an ARF for you. Best of luck in your endevors.

Mark Shuman