Cox .15 Tee Dee is still a reasonably powerful engine, and IMO up there with the plain bearing sport Schneurles. I found that to be true with the older cross scavenged Enya .15-III TV. I replaced the OS .15FP-S and 8x4 prop with the Enya and 8x6 prop on my Ringmaster Junior, (bolt pattern is close enough), was getting the same lap speeds running a wet-2. This is at our 4,300 ft. elevation. Downside was weight of engines, a little hefty for the smaller Ring even without mufflers.

Regarding Ring Jr. with .09 Tee Dee being light in wingover, may be going to 42 ft. lines? GCB was using that length on his Ring Jr. with Enya .09 engine. Tee Dee is a tad more powerful, may be experimenting with repropping might provide better thrust on 50 ft. lines?