The Tower 61 muffler is 41 mm mounting bolt center to center.
The Evolution 40, 45, & 46 have the same muffler mount dimensions as a OS 46 FX.
Can we asssume that the Evolution 61 is based on the OS 61 FX?... The OS is listed as being 43mm center to center.
Maybe you can measure your Evolution to see if it is 41 or 43mm?
http://www2.towerhobbies.com/cgi-bin...?&I=LXVH43&P=Z
Enjiy,
Jim