If you dropped the drain screw down the shift shaft hole then you could maybe drop the lower unit to retrieve it and while you're there check/replace your water pump impeller. Whenever you're working around carbs or motor controls slip a clean white rag underneath the carbs to catch screws and things that can get dropped.
I just put the screw and washer in a bagy, stuffed it in the cowel, and clamped it down. I'll worry about it on December 26 when I'm in Florida! I can remove the shift lever pretty easily and get it in; or I can pay my 8 YO $5.00 if she can get it in with her small hands.