RE: "newbie" prop question
Sandore,
I like Cubs... but you need to understand their limitations, they were designed ~1950. You can also rework them for more power, but you should feel comfortable reworking engines before attempting that. Cubs are low compression sport engines. The 20%-30% nitro and 20+% lube fuel is good. You will need to try different props. I would GUESS that a 6x2 would be best.
Your Black Widow, on the other hand, is one of the most powerful reed valve engines put out by Cox.
Fix the Cox! Get the conversion head (either Galbreath or one of the turbos), clean the needle valve area, clean the reed and housing, and make sure that intake "O" ring is good. Those areas cause the most problems.
For the intake "O" ring, cut the piece of tubing with a razor blade.
I would suggest you fix the Cox for the POC and build a smaller ship for the Cub.
Just one opinion.
George