RE: Oversizing a Tower Hobbies muffler for an O.S. 50 SX.
Wow! I ALWAYS run the Tower muff. on OS-46/50SX, Irvine-53/ TT Pro-46 etc. and I swear by them--- Good to see you started off with an 800RPM gain!
I am not very good at fabricating stuff so I would probably have trouble extending mine like you mentioned there---
That is awesome for that fun-fly prop.!