If you can locate a Cox black 7x3.5. Anything in that range is good. A newer Master Airscrew G series 7x4 might also work well.

The best prop for the Cox 09 medallion and particularly the T.D 09 was the Cox competition 7/3 grey prop. That said after reading this thread I went into the prop collection and found 1 dozen of those props. probably no interest in them anymore but they were really good props and resemble the Thunder Tiger grey line of props. Only they predated the TT props by about 50 years.

Dennis