Jim,
That long narrow gear on the stinger puts a lot of stress on the gear plate, but you will get it sorted out.

I tried many props with my G-38/Stinger also. It seems that a 18 X 8 or 18X 10 are the best combo, the 8 giving a bit higher RPM which was nice. I had tried a 20 X 6, which gave it a lot of thrust for hanging but I didn't like it because it was sooooooo slow.