I have plans, maybe in a Flying Aces magazine, for a rubber powered control line model. I saw, at a distance, a rubber powered CL model fly at a past Vintage Stunt contest. I thought the same one I have plans for. As I recall it made maybe about a lap and a half before running out of power.
I also have plans somewhere for a freeflight model converted to control line. This kind of airplane was called a "Goat". The St Louis SAM club has a contest in October which includes CL slow flight. It requires a Goat airplane, but I don't know the rules beyond that. I think winning speeds are in the 20 MPH range.
I've never built a successful rubber powered airplane, so what do I know? I think one would have to go to a geared motor to get a long enough motor run to be much fun.
Anyway, I'll see if I can find the plans and will send them if I do.