RE: Oh,what do we do when.....
I had the same problem with my Saito FA-90TS twin. The center hole of the intended APC 14x6 prop was too big.
I solved this using some scotch tape to increase the diameter of the crankshaft (see (blurry) photo).
Just make sure that the tape is not wrinkled around the crankshaft and that it is of the correct width (too wide and it may interfere with the locknut; too narrow and the propeller may not be well supported).
Radial.